Don't just narrowly press the button and push off. Press the button and the surround area, lifts the other end, enables it to slide off easily, when you slide it.
I shoot Sony, and their top always comes loose (it's cheap to replace), but I misplace it more often. I stuck a piece of fluorescence tape on top. Everything I own is black, which disappears into the ozone.
If you work outdoors, then it's a good idea to prevent water or dirt from reaching the contacts.
I'm using the simpler Canon ER-SC2 cover. There are also generics.