Try to phase out verbal praise and encouragement as early as you can, as the dog can become dependent on hearing whether he's got the right article or not from you. When the exercise is fully learned, praise by smiling at your dog when they are returning the correct article and reward when the sit and present it to you. Then when in a trial, your dog wont be waiting to hear whether he's a "good boy!" when he's picking up an article, and doubt himself when he doesnt hear you praise him.
As someone who has had a dog stand in a pile of articles, pick up the correct one and then look to his owner for verbal affirmation - I completely agree with what ShatteringGlass said!!!
Here is my experience with the tie down method . . . It was winter and I decided to start working utility articles in the house. Thought I'd be really clever and use a bit of leftover carpet. After all, it would match our flooring and I could easily tie the articles through the carpet backing.
First article was correct. Mental moment of "Yay am so clever and frugal!"
Second article, Gavin picks incorrect article. Dog: "Hmm, article appears to be stuck in carpet. Well, I shall just retrieve the entire carpet . . this will make her very happy."
So huffing and puffing, dragging the carpet, flinging the correct article aside, Gavin brought me the entire carpet with the incorrect article attached. I laughed (which in Gavinspeak means good job) and completely undermined any "training" that was to occur that day.
I know a few people that have had success with the tie down method, but we changed our plan after the carpet debacle. We started with a small pile, squeeze cheese and only rewarded correct attempts.
Good luck! Utility is fun!!!
PAM Guardyan's Gavin, VCD2, CDX, RE, AX, AXJ, AXP, AJP, TD
PACH Guardyan's Helki, CDX, PCDX, RA, MXP3, MXPB, MJP3, MJPB, CGCA
Guardyan's Kamikaze BN, CDX, RE, OAP, OJP
Guardyan's Kricket BN, CD, RN, NAP, OJP