We held an experiment where we emptied about 50 tot lots in the area in Oct/Nov last year - and then revisited some of them in the last few weeks and they are all still relatively empty - which makes me think either they are detected regularly or the finds in October were from years of accumulation.
We also noticed that some councils are replacing the bark chips with bitumen like surfaces which do not hold coins anymore. Soon the tot lots will be a thing of the past! Also in September most councils top up or replace the bark with new stuff which buries the treasures even further.
On any given day we can spot at least 10-12 looters working the beaches - so the popularity of our hobby is a two edged sword - and I agree - rural areas and the outer suburbs are the next fertile grounds to be detected however, I am sure our fellow looters are also thinking the same thing!