Hlp - my bookshelf spkr is like humpty dumpty

Office Depot sells cheap blue tacky stuff which when placed under the speaker corners and pressed down will certainly keep the speakers in place. Also improves the sound.

The blue stuff is called EZ-Tack, the Brits make a similar substance that has been recommended for its sonic benefits called Blue tack. I usually put something on top of my bookshelf speakers when not listening that will discourage the cat like a stack of CDs or my Discwasher record brush (one more reason to get into analog), but anything will do. If the errant feline winds up to jump while you are listening, a little aversion therapy will work wonders. Keep the squirt gun handy. Once properly trained, the problem goes away.

Blue Tack or similar product called Fun Tack (made by DAP) available at local Home Depot or Lowe's. Fastens speakers to stands so good that the entire stand and speaker will fall before the speaker comes loose.
Don't use cheap flimsey stands. Get a solid mass loaded stand, well worth the $.

How about concrete blocks for speaker stands. Let's see your cat knock them over! Assuming you don't have a Tiger, Lynx, Bobcat :-)

theres a white tack too samething ,easy to find and cheap less than $2