Sandy,
You could definitely use the wire frame, similar to a topiary frame. Here is what I would do; BUT remember that once anything is added to the frame it will increase the overall girth of the frame and increase weight; no way around it. So if there is a way to squish the frame work a little smaller maintaining the overall shape you can potentially get about the same size deer. Ok so now here is what I would do;

stuff frame with a large plastic bag (black or clear) then using something to stuff inside, stryo peanuts, plastic bags, newspaper etc., know where the opening of the big plastic bag is so you can remove the stuffing if you want later, be sure to have a small access area in a discreet spot if you want to remove it later. This inner core only stops mix from falling through.

*cover the outside of the frame with chicken wire if it is not already covered with wire.

*Tie or sew the chicken wire on with small pieces of wire (18-20gage)like a bread tie. Tuck in any rough spots.

*using Quikwall by Quikrete company you can apply a thin scratch coat first, this does not have to be thick and it does not end up pretty. Quikwall has fibers in the mix, Mix in small batches as it sets quickly, mixed with water creates a very sticky mix that can be smooshed troweled or pattied on to your wire surface. Your inner stuffing will stop the mix from falling through. This does not have to be very thick, it makes a rough surface for the other mix to stick to. Spritz to keep moist or cover in damp toweling.

*Wait at least overnight, longer if your scratch coat got a little thick; then
*When you are ready, spritz the area that you are working on, and brush on concrete bonding agent (this bonds old to new) just a thin coat is fine, it will make your next mix sort of slippery
*work in small batches to apply the finish coat.

*apply a finish mix of 1 pt cement/2-3 parts fine sand/colorant if you like, mix with water and a little concrete bonding agent to a thin toothpaste consistency and trowel with the palm of your hand over the scratch coat. This does not have to be much thicker that 1/2". Once you have the armature covered, you are familiar with the entire deer enough to sculpt areas with your fingertips or other tool to add detail or space for gems for eyes or horse hair for the tail etc. You can add to the sculptability of the mix by adding a little more bonding agent as the liquid.
*Remember the stuffing, you can pull the inner stuffing out if you like, but it likely will not add much weight overall.
Again you will need to spritz your work and cover for at least a week for it to cure and harden properly.
Will it be heavy? Yes definitely heavier than what you started with, but much lighter than a piece of concrete statuary.You can be in control of how heavy the piece will be when you trowel on the finish coat.
And in ten years you may or may not want to take deery with you.
You can ask at the special order desk of Lowes or Home Depot about quikwall, whichever store carries quikrete products. It comes in a 50# bag and goes a long way, here in WA cost is just under 15.00 per bag.
It is always nice to create something special for your yard.
Dena

How about using Jonathan's papercrete to cover them? I have been using it for various things around my garden and it is remarkably lighter in weight than concrete and sand mixes and I think it is just wonderful to work with. I have so much more control over the product with papercrete than with either hypertufa or concrete mixes. Also take a look at the thread on bears made of papercrete for inspiration.
Thanks Dena for that wonderful tutorial! You are a master of making things feel achieveable.
spiderwoman

Just thought I would toss in a couple more options. The first
is from an old tutorial for making faux boulders and rocks that
I had kicking around.
Cut a piece of hardware cloth to fit--around a leg for instance--(use tin snips/sheet metal cutters and leather gloves, or it will bite you!) Then take it off and cover the
inside with clear shipping tape. Wire it back on and coat it
with whatever mix you are using, then repeat with other areas.
This will give you a thin coat which means liteweight.

Another option would be to cover the deer with chicken wire
or hardware cloth, then take some fibreglass insulation, rip
strips off and dip in a thick mixture of cement/water, then
apply in layers. It is easy and strong.

Hope this helps.

Robb