OK, I see what you mean. I've never done this, and I've looked through my books to see if there was any help there, but couldn't find it.
Thinking about it, though, I think that if you even just crochet through one row of stitches, that would be like putting a lifeline it. It would secure the row. Maybe putting in a lifeline would be a good idea, anyway, so you can place your crochet row exactly where you want the neckline to be.
Having the lifeline in, crocheting along below it and cutting above it should work, since you'll really secure everything when you pick up for the collar.
Hope this helps!
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry