i use collars too, very easy to put on and take off. when im confident the female is preg. i close the door so the male cannot get to her and remove the collar. this is just what i like to do, to for sure prevent breed back and make mom a bit more comfy when going in to labor.
it usually is a week or 2 before she gives birth that i do this then shes closed off till the baby is weaned. i put the collar back on when i want to breed her again. i only allow the male access to one female at a time. so when one has a baby hes busy with another female. its slow and i dont get very many babies but im very small scale and in no rush to have a baby boom