Curious. The first song neither contains nor makes any reference to knots of any type except in the title. Following the first song, the second one is titled as "The clove hitch knot". Q mentions that both are on the same song sheet. Could it be that the reference in the title of the first is merely drawing attention to the inclusion of the second on the sheet, possibly on its reverse; I haven't seen any reference to the format of the original sheet.

Q is correct, technically , in the notion that "clove hitch knot" is tautologous and an indication that the writer(s) were no experts at knots. Q is also correct in that it does slip if improperly used. Its most correct use is to locate (in the "restraining" sense) a spar (any more or less cylindrical object) between two anchoring points by applying equal tension on each side of the spar. Tied loosely, this is how first aiders use it when making a wrist sling. Those of us who use it at the end of a rope to tie down a trailer load run the risk of it slipping because the tension from the load can't be equalised on the other side of the spar anchoring point. The use of successive clove hitches in this situation (using up the loose end past the first knot) usually fixes this fault acceptably but not perfectly.

Cheers, Rowan