Originally Posted by
Porteņo
There is a free version of that: take an old sock, cut the toe end open, "wear" it on top of the trousers' leg. When you get off the bike, take it off or just roll it down, keep it on and slide it under the trousers. The elastic busts eventually, and it can get ripped with use - but that's what the other sock in the pair is for!
Been there; Done that; It is not reliable.
It also does nothing to protect the pants when standing over the bike while stopped at intersections.