Any tricks to keep cats away from speaker grills?

Use the spray bottle technique,adding enough ammonia to the water so the cat can smell it on his(her) fur but not enough to be harmfull.
In additon to the displeasure of the water,ammonia is close enough in smell to urine that the cat will figure out the speakers belong to someone else.
My cat is not a rocket scientist(she's smart enough to meow when she wants outdoors) and she learned to ignore the speakers in three days.
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