Ironic that you should bring this up, as I have had some dramas with my dashmat ending up in my lap when accelerating away at lights, etc. Just tonight, I ran a piece of self adhesive Velcro hook material along front of the dash, directly under the bottom of the windscreen (just forward of the demist vents). The dashmat appears to attach itself nicely, without having to attach any of the Velcro pile to the actual mat. I'll let you know if there is any dramas.
BTW, I got my self adhesive Velcro from Spotlight. It came in around a one metre length.
The way I did it was using velcro, putting some silicon (very little) on the part that goes on the dash, and some stitches through the dash mat. Holds it well, until I took it off for good lol.
I got the shits with Velcro always pealing away when it heats up so I just went out and bought some spongey double sideded tape. Sticks really well and the heat doesn't seem to effect it.