I can think of parks where the ratio of tabs to any gold rings, would be 500 to 1. But on the other hand, you can cherry pick and get old silver. The notion/prospects of "digging out all the tabs" in order to find gold rings can be an exercise for insanity. It will get to the point, in some parks, where you're simply better off finding a cleaner park or different site.
If/when my objective is to find gold rings, I would simply head to places where the ratios are much better, and sites more conducive to gold-rings in the first place. Namely: Swimming beaches. Because if my objective is to find gold rings, then the LAST place I want to be a "hero" at, is a place where my prospects are to dig 500 aluminum objects per ring.
There's been times @ the beach after storms, where the ratio of aluminum per gold ring is zero. Mother nature has washed out all the light stuff, leaving only heavy targets. When you've been in situations like that, it's sort of hard to do junky parks for gold rings. Heck, even dry sand @ swim beaches has better ratios (and easier digging, doh!)