Securing Monitors to a stand

Short of strapping or bolting the speakers to the stand, I think the best one can hope for is preventing them from sliding off by a mistaken bump or brush of clothing or something. Even if they are bolted to the stands, a hard enough bump will topple the whole ball of wax. In the past I have used a cut up, old style, rubber type mouse pad (4 small pieces per speaker) between the speaker & top plate, it worked well.

I use Blue tack, also used flat bungee cords long enough to run from bottom of stand over top of speaker. As donjr pointed out, Blue tac can disrupt veneer. 

Atacama Non Slip Gel Pads. It won't leave glue residue.

I have found that the interface between the speaker and stand may have a profound influence on the sound.  Sometimes not and you need to experiment.  With my Harbeth SHL5s on Skylan stands, I preferred a hard interface such as Herbies Ebony Domes, althought this would be dangerous with small children as the speaker could be knocked off the stand too easily.  I ended up with 4 casino chips, which gave a good balance of stability and sound.  With my Opera Callas monitors, blu-tak sounded best and was extremely stable.  A painter knocked one over and the speaker and stand stayed together when I grabbed it before it fell.  Like anything else, you really have to experiment.  

That's scary chayro...