A properly adjusted slip lead is a simple, effective way of securing a dog without a collar. Here's an easy way to put it on.
Be sure that the handle loop of the lead is over the wrist of the hand holding the treat (or whichever hand feels most comfortable to you), so that you have the best chance of grabbing it, should the dog pull after being restrained by the lead.
Provided by the Retrievers volunteer lost dog team of Minnesota.