Speakers slipping on speaker stands

Bolt those babies down! Just kidding. Like Rar1 suggests, Blu-Tac and its cousins is the standard solution. Works great. Carefully use a butter knife between the tac and stand when it's time for disassembly.

When it comes time for removal, I suggest twisting the speaker off instead of prying with a butter knife or similar tool.

If you don't want to use blu tack, you can use cabinet door bumpers. The clear ones, they are about 1/8" and have adhesive that you can apply to the stand. When it comes time to remove them, they just pop off without leaving damage. I prefer these to blu tack because they provide a flat surface for the speakers to sit on, and they are cleaner when you remove them.

First of all, are your speakers moving because they're not level?

If they are level, and you can bolt them down, here's what I'm doing with mine. I have them spiked to the stand using Audiopoints and their corresponding discs. It tightens up everthing a lot. I then went out and bought longer bolts, and just barely seated them. This way if they are going to move, it's not going to be very much, and they won't come off of the stand.

Chuck

Another option might be weatherstripping. You have the choices of different thicknesses and densities. I've used it for years.