My guess would be the sand would get pretty nasty pretty quick and they'll
use the grass. The big challenge is keeping the cats from climbing over the
fence. Some claim that if the fence turns horizontally a couple of feet in
to the cat run at the top that the cats can't climb out. My shelter tried
this and it seemed to work on the tame cats until the ferals climbed out and
the tame cats followed. Now all of our cat runs are covered with a roof of 1
x 1 plastic mesh  supported on 1/2" metal electrical tube bent into hoops.
Our runs are a max of 20 feet wide which takes three - 10 foot lengths of
the tube to span.

We have a 10' x 14' storage building in each cat run but no heat. They all
pile up in the winter and keep each other warm. They get real hot in the
summer though so we're adding roof vents before next summer.

we haven't had any problems with the cats digging out or anything else
digging in. Our bunny hutch is a different story; they've already torn up
the chicken wire we "floored" the enclosure with so now we're going to lay a
foot or 2 of large gravel all around the edge so they can't go right up to
the fence and dig.
GOOD LUCK
Ron

What a great plan, Bob. I’m not an active volunteer, so have no direct
experience, but here are some links from UK sites:

Fencing:
http://www.fabcats.org/keepingyourcatsafe.html
http://www.foxproject.org.uk/
http://www.iwight.com/living_here/planning/images/CS-09-Snakes.pdf#search='snake
%20deterrent
'
I note that there’s an advert on the left banner of this forum for a
“Purrfect cat fence” - might be worth a look.

I also have an excellent archived article in Word format from the Cats
Protection journal, The Cat, which I’m trying to work out how to get to you
via the forum’s helpdesk. It’s similar to what FAB suggests, but clarifies it
with diagrams.

Re burrowing animals, I recollect that the RSPCA published a diagram in their
survival guide which showed fencing being driven a couple of feet or so
underground, then bent outwards underground. You’d need the goodwill of your
neighbours for this though. I’m trying to trace the extract but am not
holding out much luck as it’s several years old. On chicken-wire, some foxes
in the UK have worked-out how to chew it away from the posts. Sounds like the
same experience Ron had.

Advice on rescue start-up and cattery construction/organisation here:
http://www.fabcats.org/publications.html

All the best, Bob. There are all too many elderly cats, frequently who have
lived with their owners all their lives and bewildered by the rescue
experience. I'm reassured that more retirement complexes are beginning to
understand the benefits of allowing clients to keep their pets as long as
possible.

Kind regards

Apologies, Bob, can’t get the Word file or a link that had the fence diagrams
in it to you. If you wish to pursue, please email helpline@cats.org.uk and
ask if Elanna could forward you the message that was sent to Lorraine Egan on
Thu 3 Nov 13:59 headed-up “RE: Archived articles from The Cat – fencing”.

Had a sudden thought, re heating options:
http://www.catac.co.uk/ click Products, then Animal Heating Equipment –
heated igloo. Catac also sell vetbed to fit.