I once had a dog that I showed a few times in regular shows and obedience trials. With some help from a local obedience class, just held in a local middle school, I was able to teach this command very effectively. I could put him in a 'down stay', leave the room (or building), and return 15 minutes or so later, to see him still there, waiting for further instruction. When I released him from his stay, I would shower him with praise and usually a tiny reward treat.
I was able to use the downward palm signal, to make him stay...let's say while exiting the back door, and I wasn't ready for him to bolt. Without saying a word, he recognized the signal and responded. I never made this lenghtly, just a minute or so. Here's a short tip for teaching the stay command. http://www.dogs-trainingtips.com/stay.html