I've been using the string type for many, many years. I cut the tag ends pretty close. Reason being is that if you let them long, they tend to fray and cause tangles in your line when casting. As has been said, wet the knot thoroughly before tightening up. And I use two needle nose pliers to cinch it tight before trimming the tag ends. Rarely do I have problems with it loosening up and it's very durable as I change the depth setting quite frequently at times.
"A voyage in search of knowledge need never abandon the spirit of adventure."