Natural nails absorb moisture and dehydrate every day. This causes the nail to expand (when in water) and contract (when dehydrated), which is why they pull away. To prevent this problem, glue the underside of free edge right along the perimeter at every fill, drilling the glue off gently and re-gluing each time. This works extremely well.
If the nail has already separated, you must remove the lifted acrylic. I prefer to use my drill for this. You can also gently clip and file by hand. Then add the new acrylic on top. If the natural nail has pulled away from the acrylic all the way from the free edge to the smile line (sometimes this will happen on each side of the nail), then I will remove the nail and start over. If you check your client’s nails when she first sits down and take note of what each nail needs, you can wrap and soak off two or three nails while filling the others. By then your wrapped nail will be ready to remove. If the acrylic isn’t dissolved enough, then re-wrap and file the other nails you have already filled. When this is done your acrylic is sure to come off very easily. If it doesn’t, you are probably making your nails too thick.
As for drilling out the natural nail underneath, I like to do this as well. I think the shape of the nail I can create is often nicer than the client’s natural nail shape. However, since I usually do pink-and-whites, by the time the natural nail grows out, I will put on a new set. Nothing is more beautiful than a new set of pink-and-white nails. Plus, you can charge more for this service. — Mary Metscaviz, honorable mention in NAILS' 2003 AVAs in the Nail Technician of the Year category