Rotating camera when put in vertical position, how to cope?

[dRebelXT]

When I turn the camera sideways to take a portrait, the screw between camera
and tripod rotates a bit if I am in a 10-sec exposure. The center of gravity is too
far from the tripod mount. Tighten the screw, turning the right, all in vain though
the tripod head was stable. What can I do now?

 

[catchlights]

Try this

or something similar from Manfrotto

 

[mpenza]

or maybe a better ballhead?

 

[catchlights]

Or a Manfrotto 030ARCH HEX Plate,

If you find all these gadgets are too expansive, can consider weld your camera to the tripod head, this will solve the problem permanently.

 

[dRebelXT]

Or a Manfrotto 030ARCH HEX Plate,

If you find all these gadgets are too expansive, can consider weld your camera to the tripod head, this will solve the problem permanently.

Thank you all.

Since there are commercial solutions out there, I think I will first use less vertical
position and buy accessories when my $ are ready.