G'day
One of the most effective detectors I have and still use is the Minelab Sovereign GT, they are not sold new now but come up second hand from time to time on Gumtree and Ebay etc, but you can also try some detector shops, this is not a gold detector as such but is excellent for use on beaches and in parks, I use mine in the goldfields for relic and coin hunting particularly in high trash areas, I have never found a nugget with it but don't doubt it would ping a reasonable sized bit if I were to get the coil over one.
Just something to consider if you want to do this sort of thing, and probably pick one up for about $700 in used condition, also I am impressed by the new Whites tdi SL Pi detector, I have yet to try one out in the goldfields as a mate bought one so will try it this season, as a Pi detector it can be used in the goldfields and on beaches parks etc, it does not have a discrimination feature as such but does feature a target low/ high conductivity control that used in conjunction with the ground balance control can from what I have seen in demonstration it looks to be able to very effectively mask ferrous targets out quite well, its probably the best feature for trashy ground in the goldfields ans still be a capable gold detector, they are about $2000 to buy and come with a couple of coils, a folded mono coils and a concentric coil.
Other member might be able to elaborate more on the whites tdi.
cheers
stayyerAU