They don't tear that easy, but they certainly can tear. Mistake number one, cutting too much off between seam where tail meets on back of riser. Mistake number two, trying to stretch the tail to close the gap because you cut off too much.
I trim off a short section of the butt of the tail. This is where it is the thickest and doesn't form well. I wrap the tail around the bow and allow enough overlap to have plenty to work with.
Wrap bow grip with plastic wrap to protect bow from any possible dye seepage into wood. Wet tail, stretch over grip overlapping at back of riser and wrap tightly in place with ace type bandage. Allow to dry.
When mostly or completely dry, remove everything and spread barge cement on tail and grip (thinned is best for penetration). Leave glue to dry for half an hour or day or whatever. then spread second layer on tail. If it no longer seeps in, but instead leaves a nice layer of glue on top, put a second light coat on bow. Let dry for about 5 minutes...drink a bear to calm your nerves or whatever.
I always lay the tail down across the belly side and work it down tight into saddle of grip and then stretching and forming down one side all the way to the back. Then do the other side.
I use a white grease pen and a ruler and heavily trace a line down the middle of the grip where the seem will be. I cut there with a scissors carefully leaving some of the white ling on the grip. Now fold the rest of the tail over the white line and rub across with back end of scissors. The while line should be transposed on to the under side of flap of grip. cut carefully along line. There are lots of ways of doing this, but i found this to be the easiest.
I now mark the shape of the trip along top edge of grip and then on bottom. I will use white grease pen or blue ball point...they will both rub clean.
Now cut vary carefully along tracing and pull tail up into the razor blade to keep from scratching bow.
using a ruler, mark lined across the seam of grip at 1/4" intervals and then punch holes using an awl or tack as mentioned before. Re glue under laces and allow to dry. Sew but don't pull too hard and your done.
Use a piece of rubber like you would an eraser to remove excess glue.
There are lots of ways of doing this, but this is what has worked for me at least a thousand times.
good luck, BigJim