If that works for you, great - it's just not a viable solution for most of us.
If the OP was able to net his property, we wouldn't be talking about hawk protection.
I understand the biosecurity concerns - I just think that removing bird feeders and bird baths has an absolutely negligible impact on risk. Crows are strongly territorial - they're going to reduce the overall number of birds regularly using your property. Encouraging them to roost is going to...
Crows aren't going to bring any more disease in than the million sparrows, chickadees, starlings, and other wild birds that regularly move through people's properties.