I presented a sliding knot before, here they’re talking more about tipps what to take into consideration if making sliding clasps and which knots can be used to make designs of your own.
And if you don’t like sliding clasps try a self-made hook and eye clasp or a beaded shank button ;-)
Links:
Sliding Clasps
Here at unikatissima:
Sliding Knots
Self-made Hook and Eye Clasp
Beaded Shank Button