Unfortunately its highly impractical to create cloth tearing system (the tearing isnt the bad part its the fact that it teared and now people have to see it lol).

Using invisible walls would conflict to believe-ability just like standing on the tent would (if say you found a place you could jump down onto the tent from it should be allowed).

I think adding slippery surface to the top of the tent would suffice. So if you are on top you slide off.

To add more then a "keep off" element you could make the animation look like a wobbly arms out balancing act as you try to get off of the top.

Tearing Tents / Sliding or rolling off the top tent > Strong tents > Invisible walls - though the priority of tents to walls is just my opinion since both are implausible in my mind lol.