The trouble with most people who do the DL, and their developing related back problems, is of proper form. The Dl is a full body unit exercise, not designed for the lower back (or any other section of the body) to take the brunt of the work load. The first cause is not taking a proper warm-up, in good form. The second cause is having to lean too far forward, and out of line with the lifting stress points (mechanics/leverage). Avoiding the knee's with the bar seems to be the main problem (Sumo style can lessen this affect....though too many guy's do not use that form). Taking a bar, set around knee height, will lessen the undo tension placed on the lower back (using a power rack, heavy boxes, etc).
Dl'ing with a bar like a trap/shrug bar (hammer grip) puts the lifting stress more inline (center) with those body mechanics. Your lifting/holding the weight along side the body, not leaning forward, away from the body. BB Hack squats also put the body in a better position when lifting from the floor. The same principle applies here also, inline with the body. Even Dl'ing a heavy pair of DB's can be a better choice when DL'ing.
Any compound exercise (be it DL's, squats, cleans, push presses, etc) should be included first in any workout of serious intent. You reap the rewards in strength and power in the long run. If you do the exercise right, you will not need a whole lot more of any other exercise, with the DL as a first and prime movement. Maybe adding rows or chins, but not much more than that. Good Luck.