Here's my two bob's worth:
I made my husband a type of belt of wide elastic (not too tight around the waist) and just used a large safety pins (like nappy pins) to hold the pad in place front and back. Easy to undo the front to go to the toilet and absolutely no risk of pad slipping, or getting displaced. Sometimes he just moved the pad slightly to the side when going to the loo. When soiled, just attach another one.
Worked an absolute treat, he felt confident that it wouldn't slip or leak sideways etc., and it didn't matter what kind of shorts/briefs/boxers he wore.
I did try the stick on velcro dots for a short while, but these were a nuisance, and cost too much.
Cheers