careful what you cue...

I have a problem with my start line wait, which I have been attempting to cure for some time. My dog sits on command easily, but then gets up as soon as I look away. My start line command is "sit".
I had a light bulb moment this week, when I realised how often the word "sit" is used in our household, without a clear message as to what it means!
Now, my other half likes to give the dogs a biscuit when he gets up, comes home, wants to get their attention... you get the picture. Nothing wrong with that, you might say. Well fine, until the dogs start to bark whenever he returns, so that they cue him to give them a biscuit by barking! To stop this, he now asks them to sit to get their biscuit. “Great”, he thinks, “I've cracked it, all is quiet, and the dogs love me!” However, as soon as the biscuit is received they are up and off – hence MY problem. "Sit" appears to mean do so ‘til the treat is given, and then the exercise is over! 
Now, I'm not saying that this is the only reason I have trouble getting a wait on the start line, but I suspect it is a contributory factor. I have now changed my command and am in the process of explaining to her that this new command actually means “Your bum needs to be on the ground, and stay there till I give the all-important release command!”
This poisoning of a cue is not unique to this situation, and is a common snag with other agility training problems, such as contact training, recalls and direction commands. How often do you hear your trainer shout "Where was your release command?" 
To return to the start line, how many people do you see whose dog sets off before release? I am far from the only person to have this problem. More often than not the dog is actually releasing on body movement, rather than a verbal cue. We have inadvertently taught our dog that we are going to put an arm up, run away, twitch or some other little foible, and they are not listening to, nor waiting for, a release command, they are off!
So I have more work to do, and my advice this month – be clear on cues.