Push in the back is just about an impossible task for umpires. Asking to determine if someone is pushing, or holding ground and if the player pushed is staging is setting them up to fail.
The best rule change they ever made was making it if you touched an opponent's back with your hands it is a free kick (the Richo rule). The worst rule change they ever made was going back on that. It was simple, clear and easy to officiate.
I think you are mainly thinking of marking contests, where the adjudication is difficult, but a couple of observations.
Firstly, in relation to marking contests, especially when they involve a key forward, the number of times I see forwards literally pushed away from the contest, or held away from the contest, as the ball heads towards a pack is ridiculous - is that really allowed? I don't care if it is a push which is not in the back, when a forward is literally pushed or held away from the contest that must be either "blocking" (far more than a block really) or holding the man.
When the forward is allowed to get to the contested mark situation (see above, they often can't) then it does become difficult to adjudicate. The hand in the back rule was overkill, but the staging for in the back frees is rife. Maybe a 2 week suspension for staging might stop it, the tribunal can look at video evidence in slow-mo so not such a difficult call. This is an issue without an easy solution.
What I was more talking about is the player running for the ball getting pushed in the back, it happens all the time, every game, every team - if they don't enforce the rule this is what happens. There's no change in the rules here, a push in the back in that situation has always been illegal. They just don't pay them. If the player going after the ball is faster and you can't legally bump them then they get the ball, is this not what the rule was created for decades ago? It's a mess, if you push a player running for the ball in the back, instant free, that will stop it.
DS