Possible Clues:

• Riddle, say, of second shoe
• Device full of holes isn't rare, surprisingly
• Riddle of shoes son moved to the furthest possible place
• Riddle of ultimately mysterious coach
• Solver finally cracks nastier sort of riddle
• Endlessly tough holding falling water with this?
• Tea-maker who tries really hard?
• Son given mentor is someone trying hard
• Small person giving instruction that may be needed in kitchen
• Son's given teacher riddle