A comment from Dr. Ted Stashak's "Adam's Lameness in Horses", fifth edition, 2002. "One of the ironies of lost shoes is that the better a horse is shod, the greater the chances it has to lose a shoe". "It is in error to believe that a good shoeing job consists of a close fit around the entire edge of the hoof with none of the edge of the horseshoe showing and eight heavy nails with long clinches holding the shoe shoe on securely. " "A shoe that is fit full and fit to support the horse properly has more steel exposed at the quarters and heels, which is more likely to be stepped on, especially if the horse is not moving properly."
So... the take-away from this is that the better job we do of shoeing a given horse, the more likely it is the horse will pull a shoe. Shoes don't just fall off. They are usually pulled off.
When that 1,000 pound plus animal steps on himself, or more precisely, steps on the edge of a shoe, that shoe is going to come off! The best hope is that the farrier used reasonably small nails, created small clinches and that the shoe and nails come off clean without damaging the hoof wall. Large clinches or oversized nails increase the potential for wall damage. Shoeing a horse short in the heels (short-shod) to avoid lost shoes can create bruising at the seat of corn on a horse and cause other issues associated with a lack of caudal support.
Perhaps the worst criteria for selecting a farrier is by how cheap he/she is. If that's true, then a close second worst criteria would be how long the shoes stay on.
We're nailing steel to bio-matter and, for most farriers, doing the best we can to assure a proper fit, good nailing, quality clinches and afford the horse the best possible support we can. Even then, no farrier on earth can assure that a horse won't pull a shoe. We have absolutely no control over what that horse does the moment he steps off the mats. Wet fields, hilly pastures, muddy paddocks, fence lines and even something as simple as horses just being horses (playful) can all result in a horse stepping off a shoe. It's not anyone's fault; it's simply a problem inherent in shoeing a horse with some horses appearing to be more conformationally predisposed than others. A close coupled horse with lots of reach can be a really tough animal to keep shoes on! So can a horse that enjoys hanging a foot in a fence line and so too can a horse that is turned out in wet, muddy pastures.
So, what can we do?
First and foremost, shoe fit. The foot and the shoe must be perfectly flat relative to each other. The better the fit, the less movement between shoe and foot and less shearing force placed on the nails. Hot fitting helps to accomplish this by removing small imperfections in the shoe/foot mating surface, assuring a more precise fit.
Caudal support is often recommended/needed to assure a good base of support under the limb but can also mean a lot of steel hanging out the back of the foot. Make sure the farrier is boxing and safing his shoes!
Boxing and safing is the process where a small bevel is forged or ground into the outside edge (foot and ground surface) of the shoe. This provides parallel, sliding surfaces should the horse step on himself, catching the edge/heel of one shoe with another. If the animal is left barefoot on the hinds, a rocker should be rasped into the toe of the hinds so they will more easily slip off the back of the front shoe heels.
While we want at least some supportive steel outside the perimeter of the foot (particularly at the heel quarters and the heel buttress), some horses will simply require that the shoe is fit more tightly than ideal. This might mean shorter shoeing cycles.
The best means I've found is to ask the owner to make sure the horse is wearing bell boot on the front feet during any turnout or serious riding. The bell boots should cover the heels of the shoe and generally work well in preventing lost shoes.
Toe or quarter clips can help a lot too. This is particularly true if the horse shears nails due excess pawing.
If the horse is a chronic shoe puller, I might add a bit of vettec adhere or superfast to the heels of the shoe, building a small slope between the palmar aspect of the heel wall and the heel of the shoe. Another option is to "spoon" the heels of the shoe. This is basically forging the heels in an upward direction so they are close to the heel bulbs and present a more difficult "target" for the hind toes to grab.
A farrier may need to "experiment" over several shoeing cycles to "dial-in" the optimal solution for a given horse.
The idea of a farrier charging a fee to replace a lost shoe is not unreasonable. Neither the owner or the farrier can guarantee against lost shoes. It's a fact of horse ownership; albeit the owner has more control over environmental conditions and turnout than the farrier. There is a cost to the farrier to make a trip to your barn for such service and he/she shouldn't be expected to bear the entire cost of that trip/service. You can bet that the fee most farriers charge for to replace a lost shoe is nominal and probably covers only part of their own expense. In other words, even with a small $25 fee, the farrier is basically working for free to address the problem.
Does shortening the heels of one shoe create bilateral balance concerns? The short answer is generally, no.
The farrier trims/shoes each hoof to that capsule and limb conformation. While shortening the heel length of one shoe may effect the timing of stride (particularly the landing phase of stride), the effect is nearly insignificant and should not cause any problems.
If you are otherwise happy with your farrier's service, don't fire them over a lost shoe. You can trust that the farrier is just as frustrated with such an incident as you are and will do what he/she can to address the problem. Besides, there is little guarantee that the next farrier won't have the same problem.
Your best bet to avoid lost shoe problems? Bell boots. Absolute worst chronic case scenario to avoid this problem. Barefoot... even if the horse would better benefit from shoeing. Every great once in awhile, I'll run into one that couldn't keep shoes on if I bolted them to the coffin bone.