As long as they have to go through the cannon.have you ever tried to make a cave of sponge with several holes to help remove multiple nem's which have covered a large rock. When I moved from previous location, had 6 to 8 nem's now they reproduce every full moon. have one Large rock which may have 70 to 100+ rbts. have given away 65 to 75 already. few months later hAD ALL BEEN replaced. finally getting sticks/acros to grow....need space. $ager to try!