Regularly on guard – true soldiers follow training (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Regularly on guard – true soldiers follow training <o> N <g> U <a> R <d> T <r> U <e> (“regularly” means alternate letters only) + RE (=soldiers, i.e. Royal Engineers); as a noun is upbringing, rearing, hence “training”