Said it before, and will say it again - they should be weighed en route to the cage at the Harley Davidson checkpoint.
Simple. There would be teething problems, I know people will say "what if it's a title fight and the guy misses weight outside the cage?".
The weightclasses should be in 10lb sections i.e. welterweight is 170lb - 180lb.
I know that this is how it's always been done, but hell, we didn't have linesmen in football at one point - the best thing about MMA is that it is young enough in the mainstream to be adapted for the best interests of the fans, the fighters and the sport.
It's unsafe, and often unfair. Ben Henderson immediately springs to mind, when he gets in the cage the guy is like a MW.