What tricks have people used to fasten their wiring harnesses to the car?

The factory liked to use these little plastic push in barbed head numbers which were built into the harness. Unfortunately the barbed heads are virtually impossible to get out without killing them.

I am hoping for a better way...

Most Auto part stores will carry many OEM like or replacement part that you can use to attach your wiring. Ask to look at there catalogs for something that might work for you.

Many Electronic shop's (Radio Shack).

Also on the web you will find other store that sell many OEM parts and connectors. (Current Performance Wiring, Casper , M&H, etc..) You can ask for a catalog also.

Hope this info helps.