A great idea but it's not the main cause of kids at ER because of trampolines: the main issue is two kids hitting each other, not one kid falling of the trampoline. Say the head of one kid hitting the jaw of the other kid. That's the main issue (my source is a doctor friend who worked at ER and refused to have a trampoline for his kids).

So I came up with a very simple rule: one kid at a time in the trampoline and I were to see two, I'd disassemble the trampoline (and as the kid saw me assembling it, she knew I meant business).

But yup a hole in the ground to lower it sounds like a good idea too: that and a rule of one kid at a time.

A trampoline can be endless fun for kids. I got one for free from my neighbor (who was very happy to get rid of it) and a few years later I ended up giving it away when I moved.

That's why I compared it to a similar stunt on regular ground. That kind of horseplay wasn't allowed in my household, or really anything we were into as children, so my parents could let several of us play on the trampoline at a time, although they had to be more careful if we had someone over.