If they are already pregnant, then there's no need to take him out - stable doors and horses spring to mind
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If you don't want them to get pregnant, then you'll have to either take him out or have him castrated. The vet will do it for reasonable cost, especially if you take Larry to the surgery. I assume you bought them as grass cutters rather than with the intention of breeding since you thought he WAS done, so castration would seem the most obvious route to me.
And yes, they could be pregnant - although sheep are seasonal breeders, you'll get some that do their own thing regardless of the calendar. If you deal with Larry now, you have a maximum of 147/150 days of waiting