Don't be. He's just exhibiting natural behavior.
"Many toys can address the instinct to kill and dissect. Toys that squeak and have floppy parts are great for shaking to death. Pulling the innards out of a stuffed toy is an enjoyable dissection project for many dogs, or you can use old pieces of fabric or socks to tie knots around squeakers and cookies."
- Emily Keegans, Seattle Humane Society
Jeff Dentler, CPDT-KA, IAABC-ADT, FFCP, CTDI