Join Date: Aug 2006
Location: San Francisco Bay Area
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They need to be physically separated to prevent pregnancy. (An ex-pen will NOT do justice in this case; dogs have bred through wire fencing, ex-pens and crates.)
From the time she first came into season until it is safe to allow them together is approximately 3 weeks, but you probably want to take her to a repro vet to verify that.
If you put her in a pair of bitch britches/diaper and put a belly band on him, you will help slow things down a bit, but you will NOT prevent pregnancy. Dogs are as bad as rabbits when it comes to procreating. The drive is very strong.
Keep in mind that if you allow your bitch into the yard to eliminate, you may even get strange dogs jumping the fence to get to her. Yes, it can get that bad.