Yes, necks are just so wriggly! It helps if you can turn the head towards the side you're injecting as that loosens the skin. The problem with that is that if you've got somebody else holding the head, it's really easy to prick them by accident (It never actually happened, but I always worried it might).
The armpit is easy because there's no wool. However they often come up in lumps at the injection site, and whilst not serious on the neck, I think an armpit sore could be really painful.
Our vet advised trying over the ribcage, which worked easily enough this year. Does anybody else do that?
We use a
Sterimatic injector for heptavac.
It took some getting used to, but I wouldn't be without it now. It makes the job so much easier for a beginner IMO, and significantly reduces the likelihood of self-injection. The needles and steri-caps are expensive, but this year we just used a standard disposable needle with it and changed needle a couple of times, which worked fine
.