heres how its done:
get a U-BOLT
take of your clamps and put the u-bolt on the bars which are on the forks.
tighten the u-bolt a fair bit take of the u-bolt and put clamps back on and tigten, if its still coming loose put on the u-bolt back on and tighten a little bit more, put on your clamps and if its STILL coming loose, repeat the process of tightening the u-bolt on the bars.
U-BOLTS LOOK LIKE THIS: