I usually remember to fold over the edge, but I don't tape many things, so usually by the next time I try to use it it's been ruined in some way.

I've had good luck with tape dispensers. I know one might think of them as mostly for scotch tape (I know I used to) but, scaled up effectively, they're great.

I haven't tried them for duct tape, but i imagine its gluiness would interfere with functionality.