Legs Locks Loose
-It is possible that you are overloading the tripod, thus causing this problem (check specs on tripod model)
HOWEVER IF YOU AREN'T....Giotto uses (2) different leg lock designs..., quick release (normally adjusted by a socket wrench) or rotary (screw locks)!
- If tripod uses screw locks, sometimes foreign material gets into the mechanism and either damages it or prohibits from tightening!!!!!
Note: rotary locks are easy to maintain & if you need parts..., they are user replaceable and usually inexpensive! (contact Giottos distributor in the country you live in)!!!
BUT FIRST!!!! (often problem is caused by dirty lock mechanism)
-carefully unscrew the leg lock (that is slipping) until it separates from the leg higher leg section & carefully pull out the lower tube (at the top of the lower tube will be 'shims' that are part of the lock mechanism).
-Look closely at existing 'shims' do they show signs of cracking, of a build up of dirt, etc. (if damaged they will need to be replaced)
-if shims are undamaged..., use rubbing alcohol & a clean cloth to clean shims and both the tube they sit on and the inside of the tube they slide into.
-once both sides of the tubes and both male & female threads of the locking mechanism are cleaned..., place a light coating of a light oil into the threads (sewing machine oil, bike chain oil, etc)...., do not get oil on the shims!!!!!
-replace locking shims back into position and carefully slide leg tube back into place..., then screw locking collar on (this should not take any force..., if while threading lock collar back on..., it seems tight..., back off collar and check positioning of shims). Repeat procedure!!!
Note: in most cases with rotary locks, problem is purely a maintenance issue, cleaning usually fixes the issue!!!