I have 3 dogs

1) Deuce - ball crazy, male, lab mix
2) Titan - 3-4 year old GSD rescue that we've had for about 5 months
3) Lexi - young, female boxer

I have a pretty good understanding of what makes them all tick but I'm still figuring Titan out. I've noticed a behavior of his that I'm a little confused by. He has zero interest in chasing a ball. He has very little interest in playing with the tug. To most people, he appears to have zero prey drive. I'm fine with that because he was rescued to be a house pet, nothing more. But when I get the 3 dogs out and let them play, he seems to have a "chase" drive that looks an awful lot like prey drive to me. Basically, the only thing he'll chase and bite is a moving dog. He does it playfully, and will "leave it" on command with no arguments. It looks like he wants to play, but he actually bites them sometimes if I don't put a stop to it. The female and him usually play pretty well, but my male lab mix (top dog) will put him in his place if I don't.

This seems to be the only way I can get Titan to really get out and get some good exercise. So my question is... should I put a stop to it all together or allow him to play rough but just keep him from actually biting? Like I said... he has excellent control/restraint and will "leave it" reliably and without hesitation. Any thoughts or input would be appreciated.

I should also point out that all 3 are wearing e-collars anytime they're allowed to run around like this. On the rare occasion that any of the dogs hesitate when given a command, I still have an effective way of correcting them.

What you are seeing is pretty common with rescue dogs, especially one that have not been socialized, or those that have been handled roughly.

I have allowed supervised, controlled rough play. I allow biting because it is a play behavior, but I draw the line at growling (which to me indicates stress and/or aggression).

The dogs that I have handled that show this behavior have developed prey drive from watching and interacting with a normal dog that plays with a toy.

The way I've seen it is the dominant dog will put the rescue in its place and ignore it. Frustrated and still wanting to play, the rescue will lunge at the nearest toy and begin to play.

Makes sense. Sometimes while I'm playing tug with the lab, Titan will bark from a few feet away. It's obvious that it's a frustration bark, but I'd never thought of using that to my advantage. I'll try to use that frustration to build his prey drive next time. I'd really like to build him up to the point that he would play more enthusiastically with normal toys. I want to make sure I can keep him healthy as he gets older instead of turning into an old couch potato.

My biggest concern is that I could be encouraging a behavior that could turn into a fight.