In an emergency, when the only collar you have with you is a slip type, you can change it to a non-slip collar simply by locking the two rings. This can come in handy, for example, if you want to temporarily tie your dog in the shade while you change a flat tire, or if you stop to eat a picnic lunch.
Fig:1
Hold the collar by one ring, pick up the other ring and hold both rings in one hand...
Fig:2
drop the folded collar through both links...
Fig:3
... and let it fall all the way to the end.
Fig:4
Test to be sure the collar will not act as a choker. One ring will be dead. Pulling on the other will unlock the collar. If you are using a properly fitted collar, it should be just big enough to slip easily over your dogs' head without being loose enough that it is liable to fall off.
Good luck with your training!
Neil