So there's this thing with towers that makes it so you can basically beat a tower with taking 2 hearts to no damage by just doing the tower downwards in stead of up so I think towers would spawn slight under ground where you can only see the tip above ground and that the boss monster spawns at the bottom. Currently the easiest way I've found to beating towers is just to use water to go to the top mine a block above the spawners and place water forcing all the mobs away, breaking the spawner, going back up and doing it to the other spawner, then after getting 10 keys I go back up and make myself a 4 by 2 wall to crit the boss without it hitting me a single time

TL/DR: Make some way to not be able to place blocks during boss, move tower slightly under ground, and place boss spawner at the bottom