Cover for Attacking full backs

Hi. I'm wondering what role to assign a central midfielder/DM so he'll give defensive cover on the flanks. I'm playing 4-5-1 with 1dm and 2 central midfielders and 2 inside forwards on the flanks. My full backs are on attack duty and I keep getting badly exposed in the flanks. I'd like my central midfielders to cover the flanks but cant seem to find very effective roles for them. My DM and one CM have high stamina and decent defensive attributes.

This kind of 4-5-1, actually a 4-1-4-1 with 2 CMs, dont use to permit a huge advance with the fullbacks. If you want to attack more with the fullbacks you must play with 2 DMs for the cover.