"Crossing the Rubicon" is a term with political and historical connotations, particularly in being deemed the point of no return in making a decision. Crossing the little stream in this park is not as momentus a decision as when Julius Caesar decided to take his army south to face the Roman Republic, but I do refer to it - in tongue in cheek manner - as the Rubicon anytime I walk my dogs here.
Trefusis Park is just one of many city parks dotted all across Plymouth. Lots of dog walkers are here, providing plenty of opportunity to try out your "pretend to tie up my shoe lace" technique to ward away muggles. Wear some water-proof foot-wear, as you could step into water here - if you get lucky, the Rubicon may be dry.
I had previously placed my first cache in this park - I hope this one to be more successful in terms of a longer life. Please replace the stone and place back as found. It is a small container, with only enough space for a small TB. You are looking for a small blue pill-box container.