Safety pin. Wrap your pants leg snugly and pin it.
Bicycle clips have been popular for like 100 years. They do work if sized properly. Every bike shop used to have several sizes.
Toe straps or velcro straps are pretty good.
Those snap bracelet things aren't secure enough. I've probably lost 10 of them (VDOT gives them away).
As overwrought as it seems, that Leg Shield thing looks effective and convenient, and would protect your pants from road dirt.
Expert as I am with all this, I still have two pair of pants awaiting repair. Go without "just for a short trip" and you will pay!
Once you solve the pants leg problem, you can worry about wearing out the seat and crotch.