I do think you relax more over time like Helen says, but I don't think you can ever switch off with a cocker otherwise they take advantage
I also think our cockers train us too over time
Ben (who is 10) will give me a certain 'look' before he rolls or eats something he shouldn't as if I am watching him he knows I will whistle him for a recall rather than letting him roll, he knows a whistle recall gets the good treats, he also does mock runs when he will suddenly pretend to 'chase' something even if there is nothing there, I can tell as he goes off at speed but runs in an arc, he is just prompting me to do a recall if I haven't done one for a while
so who is one step ahead here - me or Ben