How do you waterproof bearpaw boots?

The best method is with Duct Tape, but plastic bags work in a pinch too.

If you're waterproofing sandals, I'm assuming they're made of leather or some material that you don't want to get wet, in which case duct tape and plastic bags are not a good solution, since you probably want your sandals to look good. So, try a waterproofing spray, like Nikwax or mink oil. They will waterproof your sandals without changing how they look.