Coleman elected to keep faith with youthful duo Rhys Bennett and Ryan Edwards only to be met with an avalanche of goals against in recent matches.
Saturday's 4-2 loss to Aldershot was the third time in as many games that Dale have let in three before half-time and they have been breached on 13 occasions on their way to four straight defeats.
"It is the third week running we have conceded three goals in the first half," Coleman told the Manchester Evening News. "We have proved over the last four games that we are nowhere near good enough defensively.
"I have to take responsibility for signing those players and playing them. Maybe, in hindsight, I would have used more of my budget on an experienced centre-half.
"The initial thought was that they were going to be good enough, but it might be that the exposure to the amount of games has caught up with them."