Towers are an interesting option. Was a half thought early on, but wasn't suitable for the Jam time frame.
But with a step back and re-evaluate, it could be back in the mix :).
right now I'm thinking about goals/levels to reach certain sizes,.. and collecting ZomBits (currency) to spend on upgrades,.. more difficult arenas to navigate around,.. As that progresses further, the turret option might be a nice option to consider :).
thanks for playing and the feedback, its much appreciated! :)