This is how we've done it with good success, for both sport and practical training.
1. Train the out as a motivational exercise. Dog grips, fight stops, give command, dog will eventually let go, praise and animate the prey object again rewarding with a tug and giving the dog the prey item. Food can be used to hurry the process along with pups.
2. This basic rule applies as training progresses, but as the dog's drive increases and he gets older it isn't as effective. . .and that's about the time when the dog's grip is set, his drive to bite is HIGH, and he is working on a helper. At this point when the dog will grip like a devil and fight like a devil, and hang on the decoy till the out command is given, I will start using the e-collar to enforce the out. (I will also increase or decrease the time the dog sits holding the helper till the out is given. That way the dog doesn't automatically out the second the decoy freezes.)
That's the key to a fast out IMO. The dog learns what out means, the dog learns that out will bring continued reward most of the time, AND the dog learns that if he doesn't out he'll be corrected every single time till he releases.
That's the basic principle, you use the dog's own drive as motivation to release and the dog's desire to avoid correction to enforce it. This is the same as you would teach almost any other obedience command.
3. The next step is to work the out with greater distractions around the dog. In different locations. In different positions. With different decoys, Etc. (I've only ever had a problem with one dog doing early outs, and that was fixed by having the decoy drive the dog like a demon if the dog released the bite before the out command was given.)
4. Finally, the out up to this point has been given when the decoy stops moving. After the dog is solid working the out on a still decoy, while working the decoy in various levels of drive and aggression, it's time to introduce a higher level of distraction. . .decoy no longer stay's still and the out command is given.
Over a slow progression you work the out while the decoy distracts the dog.
First we have the dog to a short bite and the decoy fights for a second then pauses. . .and slowly walks backwards with the dog on the bite. Work outs the same as you always have, with a reward and the e-collar.
Build up in a slow progression till the dog will out off of the decoy no matter what he's doing. Sure, after a while you have to use a higher level of compulsion to get the dog to out off of a fighting man. . .especially when groundfighting I've found. . .but it's worth it for the practical dog to have to out off of a screaming and fighting person.
I'm very grateful that my bitch has a very solid out command, it saved a contractor who entered my home and backyard without being invited from more of a bite than what he got. You just never know.
If you're dog is tough, if your training has been good and you nip problems in the bud as the crop up, you can have a dog out off of a fighting decoy without loosing much of anything in the dog's desire and fighting attitude.
If your dog isn't so great, I'd save my training time for other things. But teaching an out off of an active decoy isn't a big deal, nor is it difficult.
How effective my training will be when my dog is really in a serious fighting situation I don't know, but you can only do what you can do.