I've used Allflex tags, medium size, for years and have had about 4 lost. One was lost when the pony bit off the lower half of the ear, tag and all. I place mine just below the center of the ear, above the vein, and closer to the skull than the tip of the ear. I haven't had any tags were the front and back separate, though I have had a few sheep that I purchased that had the tags come apart. I make sure to clamp the tagging pliers firmly. When I've had doubts, I put the pliers back onto the tag and crimp it again. I don't think you can squeeze the pliers too tightly. It doesn't make the lamb happy but it gives me a measure of comfort that the tag is secure.