When fitted properly, a Martingale collar, more commonly called a “no slip” collar, is wonderful for transport dogs. It makes it virtually impossible for a dog to get out of his collar.
So what is “fitted properly”? You need to make sure that the collar is small enough on the dog that the looped portion, when pulled taught by a leash, closes the collar to the size of the dogs neck. If the loop doesn’t pull the collar “closed” around the dogs neck, it is useless.
You need to use care and make sure the leash is attached to the correct ring. The ring on the looped portion is where you want to attach the leash.
The no slip is nicer than a choke chain because it releases easier and doesn’t cut into the neck as sharply. Also, because it is fitted to the dogs neck, there is a stopping point at which the collar is no longer choking, unlike a choke collar, which has no stopping point. When properly fitted, the collar closes to within an inch of the two side rings touching, but they will never touch.
One day, hopefully, all rescue dogs would travel with a new no slip collar and leash.