At our barn it's just my sister's horse and my horse and it's on our property so there aren't any rules aside from, "Don't be an idiot."
A few months ago we had a friend boarding their horse at our barn and the rules were basic for them. They were a free board as long as they kept with the terms of the agreement which were as follows.
- Lock all gates (which they violated)
- Feed horses at night (which they violated)
- Pay for your own feed (they were good on this one...mostly)
- Clean your own stall (they were...fair on this one)
- Pay your own vet bills (which they violated)
- Don't touch horses that aren't yours without asking (this one they listened to)
- Use common sense (this one, if you don't count the other rules applying, they were good at lol)
We have the Michigan Equine Law posted on the gate to our pasture and a big sign that says, "RIDE AT YOUR OWN RISK" posted on the entrance to the barn itself.
Oh, and their horse is no longer at our barn for hopefully obvious reasons. My mother told them they needed to find another place to keep their horse because their lack of attention was endangering our personal animals. Suffice to say there was a reason they had a free board
and the animal has since been sold.