I don't know this other plant that was mentioned, but holly bushes might be a good idea. You can buy them in pots already relatively large, so they'd be less likely to be trampled, and they're a tough, easy-to-grow plant. They're pretty bushes with loads of red berries in the winter, but the leaves are very rigid, and those little pokey ends HURT!
As for the axel grease, that reminded me of something I did in my classroom a couple years ago: I had a couple boys in my class who, as they exited the classroom every day, liked to jump up and grab the door frame and do 10-12 pull-ups. The three of them would purposefully rush to the door and take turns doing this. It was a problem because while they were using the doorway as their personal gym, the rest of the class was caught inside the room, unable to exit, and it was turning nasty. Being 17-year old boys (idiots), they thought this was terribly witty. I think they believed the girls'd be impressed, but they didn't seem all that turned on. I got tired of telling them to stop and being ignored, so one day I smeared the top of the doorway with Vaseline. The first boy who jumped up and grabbed the doorway fell right on his butt and complained loudly that he had gunk all over his hands. The rest of the class loved it, and the problem ended.