Anyone have any problems getting it to stay put? It seems i have to shove it back towards the spokes at least once per ride. Any tricks?

Yes - I have just had the same problem with my new Polar 720 sensor last week. Had the speed sensor mounted about half way down the front fork and found that the sensor kept "creeping back" away from the magnet. Just moved it as high up the fork as I could get it and that seems to have dome the trick. The blade is a little thicker and this seems to give the sensor a slightly larger base to rest against and hence no more creeping. Also if your spokes allow it use the small plastic coated magnet as this seems to "stick out" more than the screw on one.

Mine has been on since Feb 2003 and hasn't moved, heres the trick : Inside the Polar box there are some black rubber patches with adhesive backing. Place a strip over the front rounded edge of the fork. Tie the sensor on, with cable ties. Place some super glue on the section of cable tie that touches the rubber patch. This will hold the sensor in place but will not damage the frame as the glue is only touching the rubber strip. This obviously works for the cadence sensor also.

CHEERS.

Mark