How exactly do i keep maggots from coming back in my guniea pigs cage?

ive had a hamster before no problem and ive had this guniea pig since easter but last night i went to clean out its cage and found it full of maggots from flies it looked like and i cleaned it out good and checked the piggy out and check its butt like i heard and its clean. but how do i keep them from coming back cuz that was just nasty