Terri1nd, can you put 1/2" hardware cloth over your garage windows? That way the windows could be open as far as you want for more ventilation, but no predators could get in.
It can go on the outside, if you need the inside clear, to open the window. We usually use washers and wood screws to attach it, but you could use strips of wood screwed down over the edges, instead. That may reduce the number of holes in the wood. After the chickens move out, just unscrew the screws, add a dab of putty and repaint the frame.
If your husband doesn't want to do that, the other option would be to make a framed piece of hardware cloth that's fitted over the window on the inside. It would be hinged and have a sturdy latch. When you needed to open or close the window, you would unlatch the hardware cloth's frame and swing it open. If you do something like that, make sure you use wood screws to attach the hinges and latch.
It can go on the outside, if you need the inside clear, to open the window. We usually use washers and wood screws to attach it, but you could use strips of wood screwed down over the edges, instead. That may reduce the number of holes in the wood. After the chickens move out, just unscrew the screws, add a dab of putty and repaint the frame.
If your husband doesn't want to do that, the other option would be to make a framed piece of hardware cloth that's fitted over the window on the inside. It would be hinged and have a sturdy latch. When you needed to open or close the window, you would unlatch the hardware cloth's frame and swing it open. If you do something like that, make sure you use wood screws to attach the hinges and latch.