There is a chance you can use:
a) an ultrasonic frequency that will repel the invaders. Devices are advertised with the claim they will repel rodents, etc. Whether they work is debated.
b) a recording of predators (mouse, rat, owl, etc.). It may require ultrasonic sound playback. Play it a few times a day, and after a few days you may not need to play it as often.
c) find out if there is a food or oil or solvent, etc., that produces an odor that repels the invaders.