One weird thing about stuck, screw-in filters;
You can sometimes get them off by pinching one edge between your thumb and index finger and turning them, instead of grasping them from both sides like you normally would.
Doesn't always work, but I'm amazed at how often it does, even with a filter that seems very thoroughly stuck. If that doesn't do the trick, you're back to needing the Strongboy or strap type wrench.
Use a rubber mat of about 5 by 5 inches.
Put it on a table.
Put your camera filter down on top of it.
Press the camera down (firmly)
Turn the camera to unscrew the filter.
Done!
The trick is to apply forces all over the filter not just on two or three points.