Use plywood over a frame of 2-by-4s, joined together by galvanized steel wood screws to create a solid base floor for your coop. Measure the length and width of your coop using a tape measure and then cut the base to fit those measurements using a skill saw. Set the 2-by-4s about 16 inches apart on the ground with a line of 2-by-4s along the board edges.
Join the base 2-by-4 framework together using an electric screwdriver to secure the boards with the wood nails. Place two nails along each board joint. After constructing the base, screw the plywood boards onto the 2-by-4s using a screw every foot along each 2-by-4 length. Leave a small gap between the boards of about 1/8-inch to allow for board movement without having the boards buckle. The boards will prevent the predators from digging through the bottom of the coop to harm your chickens.
Build your coop walls using a thick 1/2-inch aviary wire. This wire is tough enough that predators cannot chew through it and the spaces between the wires small enough that they can't reach through and harm your chickens either. Dig a trench around your coop one foot deep with a spade along the location of the coop walls.
Place the base of the aviary wire into the trench and staple the wire at surface level to the 2-by-4s you used as your coop floor base. Place a staple at least every 6-inches along the perimeter of the coop. Continue to place the wire along the posts surrounding the coop up to the coop roof. Cut the wire along the roof-line and at the door of the coop using tin snips. Backfill the trench with soil and tamp it compact with a tamper.
Use the aviary wire to roof and side any chicken runs alongside the coop as well. Bury the wire one foot deep alongside the run to prevent access from digging animals, then attach to the existing chicken run poles. Measure the length and width of the run and cut the wire to match. Cover the run with the wire and tie it to each of the poles along the run length using galvanized steel metal ties.