How can I best repair or protect this torn cover?
There are several ways to repair, one of the easiest would be to use book repair tape. There are several different ones available through Dick Blick.
Two that I have used in the past and have worked well are Lineco Spine Repair Tape and 3M Scotch #845 Book Tape. The first is basically a cloth tape available in both black and white. The 3M tape is a thick, clear tape if you want still want to be able to see the spine.
I prefer the 3M tape (mainly for being able to see the spine). My recommendation is to cover the entire spine of the book and to extend the tape at least 1&quot; from the top and bottom. Then fold the tape down in between the cover and the book pages. Trim the foldover into a trapezoid shape for ease of insertion. Once you have taped the spine, leave the book closed for a day or longer so the adhesive in the tape can bond securely to the cover.