How would you prevent ties in NFL games?

A tie is a legitimate outcome for a sporting event.

No "prevention" is necessary.

You already got two answers.

I'd have them keep playing until one team scores, but I'd maybe make it shorter overtime periods where each period, each team has less people on the field. So the first 5-minute overtime period could be 9 per side, then a 5-minute 7 per side period, then 5, all the way down to 3. That should make it easier for someone to score.

I hate ties. I understand other sports tolerate that outcome, but an having no winner is frustrating and lame and makes for annoying complications in the record. But it's rare enough in the NFL that it's not necessarily a problem.

But the solution I'd choose would be simple enough, and have them just play til it's over. Overtime should be fixed anyway. It should be a timed period (7 and a half mins, half the length of a quarter) played to the end, and if there's a tie after that it's sudden death. If you have to keep playing on forever that's your own fault for not putting the game away earlier.

As fun as crazy ideas like the one earlier in this thread can be, or like the college overtime rules are in practice, there's no news for convoluted nonsense. Just play the game until there's a conclusion.

The OT rules in college make a lot more sense. 

And for the pros they used to make it a lot more dramatic by calling it "Sudden Death." 
Meaning first team scores no matter what or how, it's over. 
Now the team that didn't score gets another shot at it. 
Perhaps they need it to be Sudden Death again. 

College rules don't make any more sense.. but they are fun. That weird approach makes for some pretty entertaining, and some pretty lengthy, over time contests.

I just don't see what the problem is with a timed period. If you don't want to keep playing then win earlier.

Finish the match when either team scores the first points.