Hmm, would like to think it was that simple. Both Jaykay and I have gone by the size of the head and leg thickness in the past but I must say I think I have 2 ganders now when I though I only had one.

You can squeeze their underside (youtube vidoes for this) but think you only do it at day old and when they are older.
Another post here said that the males stick their necks out more (?).
I have 3 year old females and 1 year old females and male(s) - I can tell the youngsters from the elders (although I have to look carefully even for that) but I have real trouble telling the younger ones apart. Any chance of eggs from your other source? I have only 2 fresh eggs, nothing added in the past 3/4days to the nest so they probably have stopped laying now. Bought some goose leg rings on ebay the other day so I can start to ring them as it will be more difficult to tell who's who next year.
My lot travel quite a distance so hopefully it will stop them from being shot at too.