You can't lock the wheels on a Mantis, Jezza, as they're freeto roll, and don't have a spline.
I sometimes wondered about making a new wheel and fitting it against the usual cultivator wheels, but after several goes it seemed of a bit pointless excercise...
When we had 'The Patch', I used to 'drive' the engine-propelled Webb mower up the hills to get home, and that really did make a difference! With the mantis, I'd just fit four rolling wheels and as it was so light ,I could get it home reasonably safely!