Watch this video from This Old House to learn how to animal proof a house.
1 Dig 8- to 12-inch-deep trench alongside porch.
2 Cut hardware cloth slightly larger than opening under porch
3 Use 2x4 to bend a 6-inch-wide L-shaped flange into hardware cloth.
4 Cut hole in hardware cloth with aviation snips.
5 Attach one-way door over hole in hardware cloth.
6 Set hardware cloth in trench, with L-shaped flange along the bottom.
7 Staple the hardware cloth to the porch.
8 Backfill the trench with soil.