Generally, when you're using your gun, you want to keep your hands and feet close to your body (behind the muzzle) to prevent you from shooting yourself.
It sounds comical, but there was an incident awhile back where a guy ended up shooting himself in the hand during a defensive encounter. He was trying to hold the guy back and shoot at the same time and it didn't work out so well.
The most common technique I've seen for trying to keep someone back is to keep the gun relatively low and very close to the body in the strong hand, with the body bladed slightly away from the attacker and using the weak hand/arm held very high to hold the attacker back, fend off an overhand blow or push him away. The idea is that with the gun held/aimed low and the weak hand held quite high, there's lower risk of a bullet and the weak hand occupying the same space at the same time.
Obviously this is only for use in very close quarters since the gun can't be aimed very effectively. But then, one wouldn't need to push someone away or fend off a blow from an attacker unless they were very close.
It's important to keep from jamming the slide against clothing which could foul it and cause a malfunctions.
It's also important to keep in mind that a magnum revolver, used in this way, could cause some significant injury to the shooter from the high-speed gases exiting at the barrel/cylinder gap.
Here are some examples.
https://www.youtube.com/watch?v=4s8t_5VT06M
https://www.youtube.com/watch?v=lVjU_5BRAO0
https://www.youtube.com/watch?v=MqNnZKA3s3M
https://www.youtube.com/watch?v=XL4KDXXTMnU