Validate an order before Save

Hi,
I'm basically trying to validate the amount and payment amount of an order before it is saved. But I'm unable to do this. I've tried overriding multiple functions of the OrderPageV2, without success. Could someone help me with this? Or is there an alternative way to do this? If so, give me a brief of the steps to implement.
My intention is to not save the order if the amount of the order exceeds a certain amount. 
Thank you in advance.
Sushanth.