No way on earth could i train legs more than once a week. They take nearly a week to recover. When you've finished legs you should feel proper sick, if not actually throwing up. They are such a big muscle group you have to hammer the fuck out of them in the gym. If you can walk out of the gym without assistance, you ain't trained them hard enough.
Do some big compound movements, heavy as you can, then after the heaviest set, drop the weight a bit, and again go to failure. Keep doing this until the legs cant hold your weight. Then they've been done properly.
once every 7 days gives opportunity for recovery, and as this is where they grow, the more recovery the better.