What are best hawk deterrents? Have a situation here!

I solved part of the aerial predator issue (hopefully) by ordering the heavy knotted aviary netting to cover their main run area. It has 2 inch openings and measures 25 ft by 50 ft and I paid about $64 for it. Much more expensive than the landscape netting, but I wanted something strong enough to last and not fall apart.

I figured it was worth the expense because I knew that hawks could get into my yard even though I am in the 'burbs...I've seen one fly through and land on my fence BEFORE I had the chickens (I think he was hoping for an easy meal from the birds at my feeders!) so I wanted to make sure the chicks were safe from them. Also, I wanted to know my chickens wouldn't fly over the fence and get into my neighbor's yards!

I do plan on letting them out to free range occasionally in the rest of my yard, though, and I have worried a bit about protecting them from hawks then even if I am out there with them.

Glad to hear that crows, mockingbirds, and martins may help...we have a purple martin colony in our backyard that we just started this year and already have about a dozen pairs nesting there. We also have bird feeders and birdbaths so we have lots of grackles, mockingbirds, and blue jays who will hopefully help the martins scare away the hawks.