Which cichlids do you have? Lake Tanganyika or Lake Malawi? You'll have better chances keeping snails with the Lake Tanganyikans. Malaysian trumpet snails are your best bet and their burrowing habit is a bonus preventing anaerobic pockets. No other snails can easily last long enough with those cichlids.
I have mts in with my malwi cichlids, they eat some but there are too many in the tank. They burrow away from predators. Also, they usually only come out at night so you don't have to see them during the day.
i dont think it is because they are aggressive- snails are usually seen as "passive" tankmates by fish, if not as food- but because they will eat them.
MTS will breed fast enough and enough of them will stay hidden in the gravel to sustain a population