May I direct you to WaveSurfing. Also, contaminating the enemy's stats has been suggested (by changing your movement at the beginning/end of round, etc), but not seriously. -- Alcatraz
The traditional way is CurveFlattening I guess. Something which Aristocles is also very specialized at. Against a perfectly flat MovementProfile a GF gun is as good/bad as HeadOnTargeting. Of course, Alcatraz is right, so far GF guns are utterly fooled by great implementations of WaveSurfing (like that of RaikoMX, Shadow, Aleph and SilverSurfer). Look at Swiffer for a MultiMode bot trying to fool any gun by changing movement mode based on measured performance of each mode. -- PEZ