What a cow defense?

"Cow defense" isn't a recognized term in any context. It's possible you're thinking of something else, or it might be a playful or slang term with no specific meaning.

To help me understand what you're asking, could you please provide more context? For example:

* Where did you hear this term?

* What is the situation you're thinking of?

* What do you think "cow defense" might mean?

Once I have more information, I can try to understand your question and give you a helpful answer.