Bad tape - how to avoid using them
 

I'm thinking I had a bad tape, but I seek your corroboration or opinions, cuz this was scary.

I taped an event (had cleaned heads very recently before it), everything seemed fine -- no alert from camera to clean heads, as it always has done when needed. Taped another event. Went home, checked tapes. First event tape was botched -- dirty, horizontal lines, pixelated, unusable. The second event fine, no prob.

Bad tape? And that's just too scary to not know! Luckily I could reshoot a makeup for this, but dang, how can you know if you have a bad tape? Can you shoot a minute and check it? Is this something you folks have any experience with?

Lil more info: Canon GL2, TDK tape. I always used Maxell till recently and started using pro grade Panasonics cuz tape is thicker, but in a pinch had to buy tape at corner store. Also, just had Canon repair my tape heads about two weeks ago. (new idler gear ass'y, drive gear ass'y, slide chassis ass'y and AV Jack. Performed tape path adjustments, cleaned head and tap path.)

History: Since repair, shot a wedding, no problems, cleaned heads before an interview and as soon as interview started rolling, camera alerted that tape heads needed cleaning which was odd I thought since I'd just cleaned them, so I stopped and ran the clean tape again, and proceeded, no problems. Then it was this next event that got botched, and the one after no prob. The cam is a few years old now. Thoughts are much appreciated, thanks!

Some cameras have:
A- confidence heads. It will read the tape right after you record it, and show you that output in the viewfinder.
B- A return function. You can go back several seconds and watch what you just shot.
With DV cameras, the VTR rewidn + end search will do the same thing. Make sure you use the end search feature to avoid a timecode break. If you don't have that feature, record several extra seconds of junk. Park the playhead/tape in that junk area so the timecode will pickup again.

Yet another option is to record on the tape... there are some programs that can read back that tape and check for dropouts.

Not true???
I think thickness would depend on 60 minute versus 80 minute tape. 60 minute tape fills the cassette, so 80 minute tape has to be thinner (otherwise you can't fit that much tape in the casette).