My beaver hides are cracking along the edge when I pull out the nails. Is this from over stretching or from drying to fast or getting the hides to dry ?

Could be one or more of several issues.Nails spaced too far apart,stretched too tight and\or dried with too much heat(too fast).Raise the pelt up on the nails,this lets the nails pull in a bit if they dry too fast with heat.

As above^^^^^^^^or it could be the way you are pulling the nails. A properly boarded pelt should sag to the board, in middle of the pelt, when raised on the nails.

Over drying Is the key In this situation.

You can also use a pliers or edge cutting pliers with a 2 x4 to ensure You're pulling straight up.

That will work.

X2 Eagleye. This is the way I pull my nails also. Snug the 2x4 or board right up to the nails. It will help hold the hide down when pulling nails. It works for me.