Instead of buying Practice Locks to level up your lockpicking, you can go to the area labeled "Amani Catacombs", in Ghostlands. There, you will find several rooms with level 16 - 18 undead trolls, non-elite, easily soloable at level 16. In every room of the Catacombs you will find locked chests spawning every few seconds. They all require Lockpicking (1), go Yellow at (35), and go Green at (55). They are still green at (85), but they are, at that point, useless as skilling up is almost impossible with them. I just spent about 20 minutes going from level 1 to 85 lockpicking just running back and forth through the rooms on my level 19.