Stopping user changing windows mobile settings

We have a number of O2 (uk) XDA orbits running windows mobile 5 and 6. Our remote workforce keeps fiddling with then when they think that it is broken because they have not had an email for 5 minuets.

Does anyone know of a way of securing windows mobile 5 or 6 so that they can’t change settings such as network settings menu options?

All advice gratefully received.