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