debar
forefend
forfend
obviate
deflect
avert *
head off
stave off
fend off
avoid ****
ward off

The police hope to head off problems before they happen.

"They may be able to head him off before he gets out of town."

I'm on a committee where we try to head these things off.

"I'm going to take a few of the boys and head them off before they are ready for us."

In fact it might be better if I head him off before he gets to our place.

"And when the time comes, you might just head off to some place where you're still needed?"

I'll go ahead through the trees and try to head them off.

The government has been trying to head off an investigation.

Maybe you better head off in a different direction from where we're going.

"But there might have been a way to head them off."