I had a comment asking for an overview of leasing (how to find the right person, how much to charge, how often the leaser can ride, how to write a contract, etc), so here is my best advice:
Your horse is your baby, right? Of course. And no one can ride/groom/train/discipline him better than you? Wrong. If you find the right leaser, you will feel totally confident that the person working with your horse has your horses best interest at heart and actually wants to improve your horse. This is the mindset that I went into my search for a leaser with, and it worked out really well.
I got soooooooo lucky with the woman who leases Lucy. She is perfect. I have had so many people who meet her ask me, "where did you find her?!" and they are all shocked when I tell them the story. I put an ad on Craigslist one day just to see if I'd get any responses. I got a few emails, but two were serious. One was L, and one was another woman about my age who wanted to ride over the summer while she was home from college. I had advertised the lease for $250 and 3 days a week. I called it a "half" lease. The way I decided on the price was by figuring out how much per month I spent on her, including shoes, supplements, grain, her stall, hay, and bedding. It came out to about $500, so half would logically be $250. I had decided from the start that finding the right person was much more important to me than getting the full amount for the lease, and really I was just looking for a bit of help with the cost of her shoes. Anything extra would be awesome.
I wanted Lucy to have at least one day off a week so I figured I could ride three days a week, the leaser could ride three days a week, and the horse could have a day of R&R. If the horse needed more than one day of rest, I would just ride less. I put an honest ad up on Craigslist with Lucy's age, experience, the fact that she needed an experienced rider, and I also included photos. I mentioned that the barn she was at had an indoor and trails and was an adult barn. The ad was up for a week or two before I got L's response but when she emailed me, I had a good feeling about her, I googled her name and nothing scary came up on the search results (you may laugh, but this is a powerful tool!) so I agreed to let her come and try Lucy.
I was relieved when she arrived at the barn and seemed very normal (phew). She seemed polite, knowledgeable, she was comfortable around my horse, and didn't seem put off by the whole "4yo OTTB" thing. I rode Lucy first and she spooked at something and sent me flying off her right shoulder within ten minutes. I was mortified. I had never fallen off of her until then so I couldn't believe she had just dumped me in front of a potential leaser! I also couldn't believe that L still wanted to try her out. I was like, wow, this girl must be as crazy as I am! But she got right on and did great with Lucy. She decided she did want to lease her. She couldn't do the three days a week so we negotiated the price down a bit and she rides two days a week. Her lease fee covers Lucy's shoes plus her SmartPak supplements so that is good enough for me.
As far as a contract, a friend emailed one to me but I didn't ever have L sign it because the lease was so simple, and it is a month-to-month lease. The contract that I had a copy of basically states that the leaser can ride x days/week for $x/month. It says the leaser is not responsible for any farrier or vet fees. Obviously this is something that can change; a true half leaser would also be responsible for half of the vet/farrier/dentist/etc. I preferred to just keep it at a flat rate because I had budgeted for the other expenses already. It also states that the leaser is responsible for any injuries the horse sustained while under their care. For instance, if the leaser doesn't put boots on the horse and goes and jumps a stone wall and the horse gets a big gash because of it, then the leaser is going to have to foot that vet bill. I really wasn't worried about major vet stuff because Lucy is insured, though. Finding someone you can trust with your horses well-being is very important for these reasons. If you think the person is going to go yahoo-ing on rocky roads and put your horse away sweaty on a cold night, they are a person you should probably show the door to. I got a really good vibe from L and we seemed to be on the same level.
Even if you don't go with a contract, make sure you have anyone who rides your horse sign a liability release!
Honestly this lease has been the easiest thing. L has become a second mom to Lucy and she has become a friend to me. If I died tomorrow, I'd want Lucy to go to her, hands down. I know she'd take great care of her and love her and enjoy her and put up with her nonsense. I wouldn't want Lucy to sit in a pasture and be ignored because she is a pretty awesome horse and she has a lot to give, but I also wouldn't want her to go to some random stranger because she is quite particular about some things. L knows her quirks and even over the winter last year when Lucy was a rank b*tch and tried to buck us off every three seconds, L stuck with it and still rode her. At one point I didn't even charge her for a month because Lucy was being SO horrible that I couldn't believe she was even still coming to ride, let alone paying to do it! If I had been leasing Lucy, I would have said, "enough is enough!" and peaced out. Lucy really was a force to be reckoned with, BUT we both hung on (both literally and figuratively) and we were both rewarded with a pretty awesome horse once her ulcers healed and she was happier at the new barn. L rides the same two days every week, but sometimes her work schedule changes and she asks to ride a different day. I am always flexible on that stuff and 99% of the time she is able to ride whenever she wants. She also comes down every so often and rides extra days if I know I'm going to be super busy one week and I'm able to offer her the extra riding time.
Wow so this entry got ridiculously long, but in short, the great thing about leasing is that YOU can decide what is best for you. There's no magical "formula" for what a half lease is. I'd start with deciding how many days a week you want your horse ridden, then come up with the money aspect, then ask yourself what the leaser can do with your horse (is jumping ok or no? can they take the horse on trail rides? off the property? to shows? can the leaser take lessons on your horse? are you going to require that the leaser takes lessons with only your trainer?). Next think about what else the leaser is going to be responsible for. If the horse colics, are you expecting 50% of the cost of the surgery? What about yearly shots -- do you want the leaser to split those costs with you? Farrier? Then think about time. Do you want the leaser to commit to six months of leasing or are you ok with a month-to-month thing? Personally I like month-to-month because if you decide this person is not right for the horse, you won't be stuck with them for 6 months. Then think about tack. Can the person use your tack? If the person has their own tack and wants to use it on your horse, are you ok with that? L has her own saddle and I didn't mind her using it but I did ask that she have the fit checked by the saddle fitter routinely, which she has done. If the leaser uses your saddle/bridle/horse boots, etc, do you want them to clean the tack when they are done with it?
So once you have all of those answers, make an honest ad up about your horse. Say what breed/age/height/sex the horse is, say what kind of training the horse has had, any show experience, if the horse will trail ride or is it afraid of leaves and stationary objects, etc. Be honest about your horse...it will weed out a lot of people who aren't right for the horse. Say how many times/week the leaser can ride, and talk about your facility a bit. Does the barn have an indoor? Jumps? Trails? Are there shows on the property?
When you get a response from someone wanting to know more, ask for references for the person. Ask if they have any videos or photos of them riding. GOOGLE THEM...you'll be surprised what pops up. Go with your gut feeling if they come to meet you and your horse. A lease is really a partnership, so if you are getting bad vibes, listen to them!
Hopefully this info helps someone! I know it's a lot to think about, but be firm on what you NEED out of the lease, and flexible on everything else. You will find the perfect person so be patient!