I've never leased out my horse but I've leased a few times.
The last 3 times wasn't a true lease in the sense that I paid board. I just rode the horses for free due to owner circumstances. If you want my experience though ..I'll weigh in.
My first experience was a true lease. I paid full board for the summer& had use of a lesson horse. Only myself& 1 other person was riding the horse at the time. The other girl moved away for work so I decided to lease him. He was 4 and it was really fun. Nothing really to note except how hateful the barn/ horse owner was when it ended.
Next time I 'leased' it lasted for 3yrs. I rode a crazy little pony (who I'm currently trying desperately to find ..if anyone from PEI can maybe help me out?). Her owner didn't have time to ride& so I took over for her. We had an agreement that I rode through the week& she rode weekends. It worked out perfectly. I used her tack because it fit the horse (hard to fit). I was always incredibly respectful of her stuff. In 3yrs, I forgot to put her saddle away once and still feel guilty about that. I treated the pony like she was mine and the owner was great because she would just check in with me once in awhile to make sure everything was going well. Couldn't have asked for a better situation. If you know the person leasing& trust thme ..this is definitely the way to go.
My next 'lease' was a little Appendix gelding. He was too much horse for the woman so she asked me to ride him for her. I really liked him too but man he was dirty& mean in the crossties. Anyway, this situation ended horribly and really burned me for ever doing this again. I would REALLY have to know the lease was going to be like the second situation. I put a lot of time& energy into that horse& had him going beautifully. The owner got jealous of me (a grown, retired woman. Some people never mature) and ended up being incredibly hateful about everything. I would have taken that horse if she had of been able to lower his price. She kept saying she wished she could but she couldn't lower the price. I understand. He was well-built, gorgeous& really knew his job. He just needed an experienced rider. She gave him away up on the mainland. Thanks.
So, moral of all those words? Make sure the person you get to lease you either know& trust. If not? Make sure you have one Bleeding heart of a signed contract.