See, my old barn, the one I referred to earlier that I left due to bad management had this policy when I was like, 10. I only stayed there a year, then left when my trainer left and got her own barn. They did give special allowance to students who took regular (at least once a week) lessons who had their own tack. But if you didn't have tack and didn't own or lease a horse there you had to stay out.
When I went back close to 10 years later, the policy apparently was down the drain, because half the time students were sneaking and borrowing stuff from boarder's cubbies. Not a nice system.
Despite the fact that there is only one tack room for everything at my current barn, my trainer is very strict about "if it's not yours, don't touch it without permission". One of her own children went and got something one day that belonged to a boarder and was scolded for it.