No, a harness is not a secure option. Dogs can wiggle out of them with frightful ease. A head-halter is not a secure collar. A slip collar can be secure in the hands of a very good leash handler, but not when the human is complacent, inattentive, or lacks a high level of skill -- and it cannot be safely left on an unattended dog. Many dogs can slip even an overly tight flat collar.
Most better shelters and rescues use martingales now.
I'm insisting that every dog transported as part of Project Next Steps be wearing a properly-fitted martingale as the foundation of the Dog Transport Security System. We're scrambling to get enough of these as dogs move out.
Unfortunately, virtually every description and illustration I can find on the web has these collars fitted incorrectly. So I had to write up detailed instructions for the people fitting the dogs or assessing the fit on dogs who already have these collars, and take my own photographs.
Above is a standard martingale of the design one is most likely to find at a pet supply store. Ignore the brass name tag for the moment.
This is a fine collar if you are going to put it on a fairly cooperative dog, adjust it to fit, and leave it there forever. The dog's head slips through the large loop, and then you futz with the metal slider until the collar is fitted (see below).
The small loop, the one that provides the "action" when the dog or human pulls the leash taut, can be made of fabric, as seen here, or chain. They work identically. The chain is not quite as good for dogs with lots of fine fluffy hair,
There are two great drawbacks to this common design. First, most untrained dogs who actually need a martingale are not all that cooperative. At best they wiggle and fuss and make adjusting the thing an ordeal. The slider is generally sticky and uncooperative itself. If the dog is actively trying to get away, or is thinking about a defense bite, you have even bigger problems.
Second, there's no way to get the collar off the dog quickly. I don't like these for dogs who are going to be playing with other dogs. I've had dogs get their jaws under another dog's collar in play, twist, and be stuck with both dogs panicked. I've been able to release them quickly by unsnapping or unbuckling the collar. With this collar, you'd best have a pair of shears and a spare collar if this happens.
The collar above is one I whipped up at home in a few minutes. I started with a cheap buckle collar and added two welded O-rings and the martingale loop with leash ring, made from a piece of matching nylon leash. When it is on the dog, it operates identically to the standard buckle-free design. But it goes on the dog in mere seconds, and is very easy to adjust to the correct snug fit.
Notice which ring the leash is attached to. If you attach the leash to any other ring, you are circumventing the function of the collar. The dog will be able to slip it.
The original D-ring, down by the buckle, is the place to hang the dog's tags. If you put the tags on the ring the leash clips to, they will be annoying and in the way. And you run the risk of accidentally clipping the leash to a split ring that holds the tags. Happens all the time. These rings pop open when loaded, generally when the dog lunges unexpectedly.
You will occasionally find commercial martingales with a metal slider to adjust size, and a plastic side-release buckle so they are easy to get on and off. They have less range of adjustment than the standard no-buckle or a metal buckle design.These work well when there's a human holding the leash. But you should never tether an untrained or flight-prone dog to a stationary object using any collar with a plastic side-release buckle. These buckles will break easily under shock-load, i.e. when the dog lunges.
The photo below shows the incorrect fit that I usually see on the street and even illustrated on websites:
Notice how the two "live" rings almost touch one another when I pull up on the leash. If I pulled a little harder they would touch. Rosie could back out of this collar if she wanted to or if she was panicking. (Rosie never panics, but she agreed to be a model for a dog who might.) It is too loose.
Here's the same collar, adjusted as snugly as I could get it, with even more tension on the leash:
See how the rings have a couple inches of webbing between them when the leash is pulled taut? Rosie couldn't back out of this collar with all her considerable wiles.
By the way, martingales are not just for shelter dogs and freak-out candidates. I recommend them as everyday + training collars for a great many dogs. They are the only training collar that is safe to leave on the dog all the time. The circumferential pressure that the dog experiences when the collar tightens is much more communicative, and simultaneously less uncomfortable, than the point-pressure on his throat when the leash goes tight with a flat buckle collar.
A prong collar is nothing other than a martingale fashioned out of metal wire and chain. Or plastic and nylon cord. I'll discuss use and fitting of prongs here at some later date.