IIRC, the number one way to screw up your card big is to use a cheap card reader, or to use a cable from the camera to your computer, and have the battery go dead. The next best way to screw up your card is to delete images haphazardly or in total instead of formatting cards. I most recently purchased a 64GB & 32GB 1066x Lexar CF card ($100 & $50, respectively). Expensive for the size and speed.. they are UDMA 7 compliant. I believe the 7D Mark I has a firmware upgrade that will enable the UDMA 7 protocol. I haven't deleted a single image on mine. Instead, I upload them all to the computer, delete them there, put the card back in, and immediately format it. Always, always, ALWAYS format your cards when putting them back in. This not only gives you a clean file allocation table, it maps out bad sectors on the card and remembers not to write there.
If you buy a Lexar card, it comes with recovery software. IDK if it will work on your Delkin or not but its worth a shot. Back in the day Lexar used to promise that if one of their cards fails, they'll not only send you a new card, but recover the data off your own card and send it to you also. IDK if they still do this.
If you ever F up your card or images, the most important thing to do is... NOTHING. take it out of your camera and figure it out later. Don't keep shooting on the card. If it gets wet, take it out and put it in a Ziploc bag with white rice. Usually images can be recovered after a quick format but the more times you rewrite, reformat, and then write again, the more likely it is to be gone forever.
HTH
