Nothing will be completely risk free in an environment which brings numerous pilot controlled rather than radar controlled aircraft into close proximity.
All you can do is to reduce the amount of blind turns those aircraft make to get onto final and separate them vertically.
There are other things like better communication.
Agree the communication element although one does then need to question the fees being charged for having a dedicated frequency..... the unwillingness of some fields forces them onto the generic safetycom.
I am not against the OH join in its pure form. That is 2000 ft agl OH, 500 feet clear of cloud so used with a minimum of 2500 agl cloud base .
How do you accurately determine the cloud base in many small airfields other than pilot reports?
Should you modify the OH to lower separations because of airspace restrictions or cloud base restrictions ? or use another joining method if neither of the two above work?
Aren't we over thinking this? What is wrong with simply being familiar with the procedure at your destination? As I said before Waltham OH join is nowhere near 2000ft QFE, the OH join height is only 500ft above circuit height and is arguably one of the busiest GA fields in the country, yet it has few problems.
In fact if you follow the process it seems hard to see why there would ever be an issue.
You seem obsessed with a standard joining height that you suggest falls apart with a low cloud base and people arriving at different heights?
Firstly you can all still use the radio and explain the height and position that you are arriving at in order to remain VMC and secondly i'm unsure of the type of people that would willingly try and arrive at this point with a few feet of separation.
Whatever system is in place there will always be a senario able to catch out and foil the standardised norm. No rigid system will be a catch all. Ultimately see and avoid works just as well in the circuit as outside of it and aviate, navigate, communicate...
Isn't it the case that actually regardless of the system bad airmanship is bad airmanship and arguably No.1 on that list is the lack of a plan.