If a property owner gives me permission to trespass for any reason related to hunting and fishing I always go back and offer my thanks. I also have been known to return with a small box of See's chocolates as a gesture of appreciation. This was something my father taught me and I think it represents the spirit of respect and being thankful. I imagine a legally fresh killed salmon (hatchery type) would also go well as a gift. I just am not that good at saltwater fishing yet. Robert Ruark in The Old Man and the Boy said it well "There's more ways to kill a cat other than choke it to death on butter."