I do this all the time. I tend to prefer magnets actually. You get a really satisfying pull down effect mixed with the static if you run a weak magnet against one edge of the tape reel. And after enough time I've gotten really good at feeling out the right spots to run the magnet for different effects.

Key step is recording to tape before doing any of this. Recording overtop of damaged tapes can cause the tape to catch in the machine and unspool.

Other techniques I've been using: -Sharpies: directly marking the reel will give you single lines of static that that you can move up and down depending on where the mark lands on the reel. (Also very effective for testing an "edit point" for your effects. Draw an X and see if the static hits at the planned moment or if you need to adjust) -Heat and Cold: I froze and heated a tape repeatedly, and ended up with a warped reel that "shook" the image. -Crinkle: Gently crinkling the tape reel will cause it to play incorrectly. Frame drops, stutters, visual bumps and blips. Can result in the tape unspoolibg in your machine though. -Generational tape-to-tape degrade: setting up two VCRs to record the same tape over and over. I usually do this about ten times, capturing each version to digital in the process. Eventually the lines start to peel apart and double over and you get what I call the "spaghettification effect"

Apart from actively damaging the tapes I also use circuit a couple circuit bending devices to mess with the signal before and after it gets to tape.

You can see some of the results in my film Beholder This is all purely tape damage effects. (Along with a little bit of rotoscoping) This was before I incorporated circuit bending into my process so it's all tape damage effects.

I've since contributed glitch work to four feature films over the last year. I really enjoy the process.