Possible Clues:

• That's not the sole way in which the army marches
• Popular bit of a dance, moving in unison
• Conforming (with)
• Not a whole foot to keep during March
• What the Foot must keep on foot
• How to march on foot
• On foot on the march
• How the dogs and cats get back just over one foot in the direction of Ulster
• Foot arch - conforming
• It may be under your tongue