Salt on His Tail
(Lay). Catch or apprehend him. The phrase is based on the direction given to small children to lay salt on a bird's tail if they want to catch it.
“His intelligence is so good, that were you to come near him with
soldiers or constables, ... I shall answer for it you will never lay
salt on his tail.” —
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894