I've always liked that rule Stevenson! haha I don't mind if you pet it out in the field and check it out, but don't bring it up to the barn unless it's an emergency!
My BO has no problem with us bringing people out to visit the horses, but if they want to ride she has a waiver (that is available for us to pick up any time in the barn and have the person sign it). I trust her completely to look after my horses, so if I don't go out I know that they're taken care of, but we had a friend who lost her horses in a freak accident. All four of us: me, my mom, our friend, and the BO all knew each other and knew that while she usually came out with us, if she ever wanted to go and groom on our horses she was more than welcome. A situation like that I don't mind, nor find it invasive if all are in agreement. (I don't know if she ever contacted her before she came out though.) My BO lives on the property and quite frankly I hardly ever contact her to let her know that I'll be out. IMO she might live there, and I do respect that, but my horses are there as well and I'm paying to virtually rent on the back section of her property. I never go up to the house though unless I'm invited or I've contacted her ahead of time. And I respect her family time (so on holidays I might go out but I make sure to not ride in the 'arena' and instead ride in the horse field or just go out to visit).
Then again it's a small place with only a small amount of boarders, and we're all pretty low key. If someone strange does show up my boss will check and see what they're there for, but honestly the only people who've done that are ones looking for riding lessons, or asking about any horses for sale. :P Also, there's the fact that my mustangX gelding has a habit of running down people with bad intentions. We had two guys who decided to hop the fence (electrocuting themselves in the process), then go and 'ride' a horse in the field. We watched my gelding run them out of the field at a full gallop and every time they tried to get back in he'd run them out again. Poor guys ended up having to be rescued by us boarders and the BO because my gelding wouldn't let them leave a corner. He seems to know the difference between good and bad people because if someone who just started boarding and he's never seen before goes out there he might be alert and watch them, but won't do much more than come and sniff them and say hi. So that's our security! lol