Things to think about when leasing out your horse?

I moving my business from my home to a commercial location, so I will be working a minimum 12 hours a day 5 days a week and won't have much time to ride Bourbon at all until I can hire some help in about 12 months. I was thinking of leasing Bourbon out to 1. Help with costs and 2. Get him some riding time and attention.

I've never leased out a horse before. What are some things I need to think about?