Squats and deadlifts and going heavy is the way to go. You can train long or hard but not long and hard and leg muscles are your biggest muscle group and take the most out of you. If you go heavy after a warm up and do a killer workout there is no way you can train the legs more than once a week,if you can do 2 you are not working out hard enough. Make sure you are well rested before the workout so you can hit it with everything you have and mean business and be agressive.
Hit the cycle machine to warm up and do stretching then do a warm up set on leg extensions then 3 sets heavy 6 -8 reps then leg press 3 sets 6-8 reps heavy with slow negitives. This guy has very good technique to study.
Then hit squats preferably with a partner to spot. Warm up set then 3 sets of 6 -8 reps heavy or 20 straight squats without stacking the heaviest weight you can do 20 with.
Then hamstring curls in first video warm up set then heavy 3 sets 6- 8 reps with slow negitives.
Then calf raises,work them to exhausion 3 sets.
On alternating weeks you slip in deadlifts instead of squats.Again heavy with over under grip.
After a hard core heavy leg workout you have nothing left and are done and may experience shaking. As soon as you finish take your whey protein and make sure you have plenty of protein in your food and rest and you will grow.