Locking down an OU to only allow creation of one object type ie. Groups

Heya,

Been messing with the best way to lock down an OU to only allow the creation of a certain object class, ie groups in a group OU and so on. Any ideas on ways this was done or can be would be helpful.

tried a mix of full control groups and deny creation and moving of other class objects but no dice.. maybe i am missing something obvious..

thanks!