How about giving the chickens some Borg-style adaptive shields, which become more effective when they’re hit with the same kind of weapon over and over again? That would encourage players to change weapons periodically, instead of just sticking with one favourite.
Favorite gun selection is better…
I don’t understand what you mean by that.
What I mean is that if you keep using the same weapon, the chickens’ shields get better at resisting it. The weapon becomes less effective against that kind of shield. Kind of like how, on Star Trek™, when the heroes™ are fighting the Borg™, they have to keep recrogulating™ the phaser™ transtations™ so the Borgs’™ shields™ don’t keep blocking them™.
This could be indicated visually by adding some colour to the barriers.
To take an example from CI5… In wave 3 (“Pedal to the Metal”), the player is confronted by a bunch of barriers. Suppose the player is using the Hypergun, which fires cyan bolts. The barriers start out grey, but by the time the player has finished the wave, they’ve taken on a cyan tinge, and the Hypergun bolts are beginning to lose effectiveness, just by a tiny bit. But if the player continues to use the Hypergun, by the time they’ve blown away barriers in waves 5, 7, and 9, the barriers are brighter cyan, and the Hypergun does noticeably less damage against them. But if the player switches to using the Neutron Gun in wave 7, it’s fully effective against the barriers, and as more barriers go down, the cyan colour fades out of them… to be replaced in turn by the bright green of the Neutron Gun, gradually, if the player continues to use that weapon.