Do you folks have any advice for my sister?

I need some help trying one last thing about keeping the animals out
from under my deck. The best choice is to have it ripped up and
replaced with a concrete patio. However, I think that will cost me at
least $10K. I'm going to get an estimate but want to try one more
thing before I do that. Right now I have at least two ground
squirrels and a raccoon living there who come out periodically in the
day/evenings.

Do you have any ideas? A good idea is to dig a trench deep enough all
around it and put in short fencing so the animals can't dig
underneath. However, that's too hard for me, and I can't buy the
fencing small enough (it's in huge rolls at Lowe's/Home Depot). What
has worked is rocks--but wherever I put them to block their entrance
they just avoid that area and dig another hole to get in and out. I
don't think I can find enough rocks to totally surround the deck.

I have hired a high-school kid to help me in a few weeks. He will do
the physical labor based on my idea. So, I have a few weeks to decide
what to try this time. Any ideas?

Thanx in advance
Jason