A sight getting bumped is a concern with any optic. However, I've probably worried less about my Venom getting knocked off than any other optic. You don't realize how small and low profile it is until you get it.
There is a fellow around this forum who builds a protective housing for red dots though if you find it to be a concern. I think his name is Gobbler something. Dig around here and you can find it. I've never felt that it was necessary, though they do look well built.