Overtime we've learned some tricks to tighten up a still's camera mount. Here is a quick pictorial.
A nifty trick we recently learned is to warp the mount just a tad. With a soft mallet give the mount a stiff jab. Try it out. This will fix any play in the mount. Flip it over and reverse the process if its a bit too tight. Obviously don't use a standard hammer!
At first I was uneasy, but this is actually a great idea. Apply "removable" Loc-Tite to a camera mount before screwing it in and it will minimize how much torque you'll need to apply to keep it tight. The nice thing, is it's removable.
We add a nylon set screw to our plate to prevent the camera from spinning if it gets hit. Using this an a velcro strap is a surefire way to keep your camera mount steady.
The final trick is if your mount is not sliding well anymore. We use a bit of nose grease to lube it up. This stuff works super well!