it's going to sound silly but i use a pantyhose on one of my pumps! it works on keeping stones,sticks etc while letting enough water threw and a whole lot cheaper then buying a new pump all the time!
One thing about pantyhose is if there's small roots and grass it will suck it in the holes of the pump and start filling up inside the housing. This has happen to me and it's a pain to get out. But if the stuff your running is clean it works well.