Sorry to jump in late, I just found this thread. We've been through this also with our mallards. The federal law ( 50 CFR part 21.13) allows for marking with seamless metal bands, pinioning of a wing, tattooing on the web of the foot, or cliping the right hind toe.
I could not find any manufacturer or supplier of "seamless metal" bands. I found seamless plastic and butt end metal bands but that's not good enough.
I wasn't going to pinion a wing cause I thought that was to severe.
Tattooing the webbing won't work up here because of how harsh our winters can be on feet. We would run the risk of having unidentifiable markings.
So clipping the toe was really our only option. The hind toe (in the young at least) is skin and cartlidge. I clip them with a pair of really sharp sissors as soon as there clipped I put them in the bath tub for a swim. It's been my experience that they throw a bigger fit just from being held than from loosing the toe.
The first couple times I was a bit squeemish but after seeing how quick and easy it was I got over it.