The only way to sex a non-autosexing goose is to vent sex it. They don't like it (Iwouldn't, either) and they sure don't appreciate your learning curve, but there's no substitute.
Here's how our ID system works:
Every bird that we have or keep for breeding has a colored metal ID band on its left leg. The color identifies the year of birth. After we run through all availbale colors, we'll have to start over, but that's years down the road. On the right leg, each hatch is designated with its own color. That color remains on top always. The second or third colors below that identify individual birds.
Here's a couple of examples:
There a bird with a blue band on its left leg and a red band on it's right leg mating with a bird that has a red metal ID band on its left leg, and a (top to bottom) yellow, red, and green set of bands on its right leg.
Blue is 2008, red on right tells me that bird is Tufts. He is mating with a bird born in 2010 (red metal ID), "Yellow Team" bird, (hatched 27 Apr 10), red and bellow the yellow is "Sally".
A bird with a red metal ID tag left foot and a blue(always top to bottom) and orange zippie on the right leg (red ID, born 2010, Blue zippie on top, hatched 13 Mar 2010) tells me this is Lucky. He's mating with a bird with a green metal ID tag (born 2009) and a yellow (hatched 18 Mar 2009) and black zippie combination on her right leg. That tells me it's Elspeth (yellow and black).
We reserve black zippies for birds intended for slaughter and orange for birds that we are going to sell and not breed. Those go on the left leg in place of the metal ID tag.
A good set of binoculars will identify birds out in the field.
This works really well when there are a lot of birds to watch. Zip ties can and do come off. They are an item of daily observation around here. It also allows us to to keep good breeding and health records