Erick,

Fly777 makes a good suggestion for mass balancing. The idea is to move the balance point forward to the hinge point.
You don't mention what type of plane or hinging material you're using but here's the steps that I'd take ranging from the cheap and greasy to the most complex.
1. Firm up the control rods, if you're using EZ clevises screw a nut on the rod before the clevis and tighten it on the clevis to reduce slop.
2. Seal the gap with clear tape or monokote, this will prevent the migration of high pressure air through the gap to the low pressure side.
3. Replace long wood or wire pushrods with arrow shafts or carbon tubes. Terminate in ball links.
3b. If you're using nyrod or similar product, make sure that the sleeve is well supported inside of the fuse so that it cannot flex under load.
4. Replace cheap-o horns with more robust units from Sullivan or Robart. If the plane's giant scale use Rocket City 8/32 links.
5. Open up the aerodynamic counterbalances and add lead shot and epoxy to balance the surface.
5b. Without aerodynamic counterbalances you can epoxy a plate or wire to the tip extending forward of the hinge line and add lead to the end.
6. Move the hinge point back into the surface (nothch the surface and use Robart hinge points to move the hinge point behind the leading edge). Look at full scale rudders to get the idea.
7. If #6 is already in use, add brass strip on the leading edge to mass balance the surface.
8. Rebuild the surfaces out of lighter material. Carefully select the lightest wood that you can get away with. If the surface is solid wood you can cut lightening holes. While you're at it, add an aerodynamic counterbalance to the surface, stay below 40% of the surface size and you should be ok.

Chris