Last year we started crimping all the leader lines. We tie the main fishing line (30 lb test) to the snap swivel but all the leader material we crimp. I found a nice set of crimps at Dicks sporting goods. I believe they were less than $20 dollars. Last year I heard some on the radio saying they lost a fish due to the knot slipping out.
Our leader material is 80 lb test. Sometimes we use 100 lb test. It is hard to find sometimes so I always buy extra.