In reply to EricpAndrew:
You can get a special "hot knife" tool for cutting nylon rope. Depending how much you have to do it might or might not be worth buying one, and you might or might not be able to borrow one from your friendly local outdoors shop.
If you are making do with knife and hob, try wrapping the rope tightly in sellotape before cutting - it makes it quicker and easier to get a neat heat seal on the end.