Add a tower that allows other towers around it to see invisible mobs. "Radar Tower" is what it would be called. It would allow other towers around the "Radar Tower" to see invisible spiders or other invisible mobs, if there are anymore to be added.
I think it's a good idea! because it is very difficult to kill the invisible monsters
But a little adjustment maybe it would be nice to set a limit for example 1x places per team :)
Yep.1 Problem though, You will only be able to place 4 of them and then all the towers would see invisible zombies rendering invisible mobs useless. Goodluck on your suggestion though and enjoy the rest of your day :)