I've got horizontal training wires running along a wall. I have a couple of young espalier pear trees and a couple of climbing roses to train. The problem I keep experiencing, is that if I use string, it tends to slide along the wire over time, rather than remaining where I tied it. Does anyone have any tricks for solving this? I wondered about crimping some small pieces of lead sheet with a string-hole drilled in it, but I suspect there must be an easier solution...

TIA
Al