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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kudos to those who wouldn't remove their children's fingernails...

my findings:
1) the scented sprays don't work. if you want to try this route, set the grills on the ground and squeeze concentrated lemon juice / fresh oranges onto them---cats HATE this stuff. note, it does wear off over time, so reapply.
2) stickiness: 2x sided tape works well. so does flypaper. and self-adhesive tile. i personally like tile---use some blu-tack to set it upside down on top your speakers--less likely to cause damage to the paint than 2x sided tape.
3) water gun--very effective
4) loud noises--a sealed jar 1/3 filled w/ coins, shaken violently whenever they get near the item, is SUPPOSED to be effective. but if you're cats trust you a lot, it probably wont work. stick w/ the first 3.
5) scratching posts BY your speakers...cats want to be part of the environment, so make the environment more suitable. condition them to not use the speakers ("bad kitty") and physically place them onto the scratching post and move their paws on the post to stimulate scratching w/ positive reinforcement ("good kitty"). also helps to spread some catnip on the scratching post to make it even more appealing.

and if all that fails, just set your cd player on repeat with the track "who let the dogs out". that will drive everything and everyone from the room, guaranteed.
rhyno

A small, low-amp electrified grid made from chicken wire (recycled from an old psychology experiment with rats), extending about 9 inches around the base of the speaker, worked very well with our cat. One good zap is usually all it takes (grin).....

Now, before the SPCA or some irate cat lover contacts me, I'll share what I really did. During the day, when away at work, I put long cloth socks over the speakers. Then, in the evening when I was home, I kept a small, hand-held vacuum nearby, rigged to blow rather than suck. When the cat started to investigate the speaker, I'd turn the vacuum on and give the cat a good air blast. Definitely did the trick -- the cat has never scratched the speakers, and she's now too old to bother (kinda like me, actually...) Of course, the cat has a phobia even today about vacuum cleaners -- heads for the hills when anyone vacuums the living room carpets -- but I consider that a small price to pay (heh, heh, heh). All in all, this thread may offer some of the best arguments I've heard for owning a dog...

my 100lb. sheepdog keeps cats away from anything.

We couldn't bring ourselves to having our cat declawed either, but after she climbed my Vandersteen 3Asigs (cloth on all four sides) 2-3 times, I kept chicken wire around them for over a year. It looked like hell but was very effective. BTW, when I up-graded to V5s (wood on lower 1/2 of all 4 sides), the cat now no longer bothers them. Kenscollick (above post) ended up with my 3Asigs, so it worked out well for both of us.

BTW, we tried the water spraying for quite awhile with only limited success, ie we couldn't guard the speakers 24 hours a day. Our Vand. 2Ces also ended up getting replaced with stand mounted PSB Stratus Minis to eliminate cat problems. Hey, we like the cat.

Cats don't like tinfoil, and it worked for 2-3 weeks on the floor around the speakers. Good Luck Craig.