A simple approach would be to make an "oversize" intake filter. The ones that come with the pumps are tiny and clog easy. For a smaller pump you can use a collander with a stocking over it, for a bigger one just a metal screen box that cages the entire pump. Don't know about the other pump questions.

Cornbuzzer, Up sizing your pump or having bigger holes in the pre-filter will not solve the plugging problem. The string algae will still plug everything up, including your pump's impeller, then you have more work to do, taking the pump apart every few days.

You will have to start pulling the string algae (Filamentous Algae) out by hand or use a stick or a toilet brush to wind the string algae around and then pull it out of the pond.

Hydrogen Peroxide (3% per volume) bought at a drugstore etc, can be poured over the string algae, at a rate of one pint per hundred gallons of water.
This should turn the string algae dark brown and kill it off within a few days, after which, the dead stuff should be netted out of the pond.
Note.Hydrogen Peroxide will not work on suspended algae (i.e "Green water").

Take a look at David's post about killing/removing string algae from a deep area of a pond.(linked below)

Here is a link that might be useful: David's post about string algae.