I tried the "lure" approach for a few sessions, and got nowhere! And out of frustration (IE - lay down is a pretty simple behavior) I decided to "shape" the behavior.
Essentially, Coco was given a "marker" (in this case a VERY VERY excited "YES!") and corresponding treat (nearly simultaneously to the "YES!") when she made ANY move that remotely looked like a dog attempting to lay down.
At first, and this no lie, she was getting treats for simply LOOKING at the ground! And if you can imagine a "flip book" of pictures that show a dog laying down that's what our training sessions would look like. Each session she would get a little bit closer to laying down. It took about 4 (maybe 5) sessions lasting anywhere from 3-10 minutes each. And I didn't introduce the cue ("lay down") until she was doing exactly what I expected from a "lay down."
And these days, she can hold a down for several minutes while we're playing catch (her FAVORITE past time.) No too shabby for a dog that didn't get ANY type of training till she was about 6yrs old!
Most dogs are super smart and whenever I get a little frustrated I remember what a dog friend of mine told a while back: these dogs continue to learn INSPITE of us!
Good luck I'm sure you'll do fine! And if you have any Q's about the "technique" I described (marker training) check out this website -
www.clickertraining.com (tons of freebies!)
Donovan