Canasia Sports

I'm new to this newsgroup, but have a question that I'd like to pose to the more experienced divers out there:  is a dive knife essential? While I have a C-card and like to scuba dive, I'm also an enthusiastic snorkeller.  The one thing that scares the heck out of me more than anything else snorkelling is getting snagged on fishing line, especially high-strength monofilament nylon line that looks almost invisible in water. It may not be too serious for scuba, but getting snagged while snorkelling could become quickly fatal.  Is it a serious concern or just my over-active imagination? I asked an acquaintance who's a very experienced diver, and he said he only got snagged once or twice (wasn't sure himself) and that it wasn't a big deal.  Also, he recommended surgical scissors instead of a knife to cut through snags.  I have a lot of respect for his wisdom, but would like to know if the other expert divers agree with him, or if there's a big difference of opinion on the matter. Another question:  if I do decide to get a dive knife, what do I need to do if I want to take it with me on an airplane without getting into trouble? Thanks in advance for the advice... Lunatim