That seam where your two pieces of hardware cloth meet on the door - have you stitched that together? Basic whip stitch with 19 gauge wire (they sell it on spools at the hardware store). I use gardening gloves with rubber coating and one or two pairs of needle nose pliers to pull wire or adjust hardware cloth as I sew. Unless that seam is really tight and you can't get something more than 1/2" in diameter through, you might want to consider that. Or you could put a small piece of wood on both sides and screw them together to secure, or wood on one side, and secure with radial washers and screws through the hardware cloth on the other. I like to walk around my coop and pretend I am a small predator and pull at anything that seemed loose or that it could open. I always end up adding more fasteners or securing it further.