Some times you cant avoid the nails and or don't want too. A large storm is going to wash the nails into the same cracks as the gold and removing them might be just whats needed to get to the bottom of it so to speak.
When Nugget shooting I always bring a pan and crevice tools and If I find a area of bedrock that has a nail line or the whole area has lead and Iron. I will pick a badly infested area dig too the bottom of the crack and pan it.
If I don't get any color after a couple spots I move on.
There are areas so loaded with lead its hard to believe there is no gold but if the crevices are full of shot and you don't get any color MOVE ON!!!!!
For sizing the target you get a real good idea just from the response range using all metal but if you switch to disc and even though you cant hear the target, in pin point it is stronger and easy to determine if it is a small surface target.( Problem in a nugget environment is you cant always even sweep two directions or get a good swing at all)
So If hunting fine gold you are not going to get it at any kind of depth anyways, you can use your pinpoint to eliminate larger items and or deeper items such as nails and only hunt the tight surface signals.
If there is a chance of larger gold around on the gram + size pieces (Depending on Depth) they are going to hit in disc mode as well.
I find I can get a 1 gram nugget to hit and id well if the soil is not to hot at 3 to 3.5 inches. Of course its pretty flat and has good surface area for its size.
Use all the Tools at your disposal find the targets with all metal and check with disc and pin point.
Nails can be easier to avoid this way.