The most important detail is to make sure that the wooden base of the sculpture (generally the hooves of the animal) is elevated from the ground. I am happy if one can insert one's fingers between the hooves and the body of the lawn / ground. This means that wood will dry out after rainfall. Most of my full size sculptures are built on a stainlesss steel subterranean frame. The frame is designed to sit on a concrete slab embedded below the surface of the ground. Once the location is determined, excavate an area a little larger than the stainless steel frame. The depth of the excavation should allow for the thickness of the concrete slab and the hieght of the subterranean frame. I will liaise with the client to establish these measurements. 
With my larger sculptures (200kg +) lifting equipment is required to be on-site to winch the sculpture onto the concrete slab. I incorporate a lifting eye into the design of the armature (the structure of the sculpture) to make the job of lifting the sculpture safer. Once in place, I provide "U" brackets that hug the subterranean frame. 2 pcs 12mm dia concrete bolts (or expansion bolts) hold each "U" bracket onto the concrete. 
The excavated area is then filled with top soil and covered with turf or any other ground cover.
Some of my sculptures are mounted on a driftwood base. In this case a concrete foundation should seperate the wooden base from the ground. The danger is that if the wooden base is set directly on earth, it might well start to decompose over the course of 5-10 years.
For large outdoor sculptures I provide a severe weather jacket which can be slung over the sculpture in times of extreme weather. What constitutes extreme weather? Severe snow storms, Arctic type weather conditions. Almost all the driftwood I use is really oily, decades dead and hard as nails which stops it from absorbing moisture hence there is no need to cover the sculpture during times of  rainfall / frosts.
If the sculpture comes with antlers, the antlers will need to be removed before placing the severe weather jacket. You will find a stainless steel ring at the base of the antlers that attaches to a lock pin - pull this out, then remove carefully the antlers. The tail of my later equine sculptures (post 2010) removes in which case the tail should also be removed before placing the severe weather jacket. If the tail is removable you will notice a small stainless steel ring at the centre of the rump which, if drawn, will pull out a pin that locks the tail in place. Best to reinsert pin with or without tail / antlers to avoid losing it.
My earlier sculptures of rearing/jumping stallions were supplied with a brace which should be inserted usually between the chest and the base of the sculpture during heavy winds / serious gales.
Both the the brace and the canvass are best set in place if you are leaving for an extended period of time over the winter months.
Every spring an all-purpose colourless wood preservative can be applied to the driftwood to offer additional protection. I use Solignum however Cuprinol (in the UK) is also excellent. In fact any decent garden shed type wood preservative / wood protector will help to protect the wood. Please just double check it is absolutely colourless before applying on the driftwood.
If the sculpture is placed in a shady area, you might find that algae and/or moss attaches to some areas. This in itself is not cause for too much alarm as it will take decades for the growth to degrade the surface of the long dead wood however often the green colour of the moss does not add to the aesthetics of the sculpture. Any standard Moss Killer should sort out this problem. Bayer offer a range of Moss Killers - either Bayer Moss Killer or Bayer Path and Patio Cleaner. Both may be toxic to plant life - a non-toxic moss killer is Just Green Patio and Concrete Cleaner which (although I have not tested it) is endorsed by the RHS. This RHS link is very informative; www.rhs.org.uk/advice/profile
Over the course of time, within a year if the sculpture is placed close to the coast, the wood will turn a silvery white colour in the salt air. The finish is surreal and most of my clents prefer this silvery finish to the original tan look of the sculpture. If your sculpture turns silvery white and you do not like the finish then a good old scrub down with hot water and patio detergent (such as Karcher Universal Detergent) will clean the sculpture back to the original tan look.
Check the area around the hooves carefully to make sure that the base of the hooves is clear of soil as this will degrade the wood fairly quickly.
In conclusion, a typical maintenance should wait for a sunny spell and follow these steps;
1) If the sculpture is set on plant life, lay a ground mat to protect the plant life, making sure that fluids will pool at a suitable place in order to bucket out excess chemicals. Set-up a walkway to allow easy access to the sculpture.
2) If needed, apply the Moss Killer, following the instructions (usually apply with a thick 4" Paint Brush). Allow to dry and scrub down the affected areas with a dry nylon brush.
3) If the grey/silvery look is not desired, scrub the sculpture down with patio detergent using a hard bristled nylon brush taking care not to damage the smaller pieces of driftwood such as the mane and the tail. If a pressure wash is available, pressure wash the sculpture to rinse the detergent then allow the sculpture to dry.
3) Apply the Clear Wood Preservative (Cuprinol for example) again following the manufacturer's instructions. Usually this entails applying the wood preservative onto the sculpture using a 4" paintbrush starting from the top moving down to the bottom, allowing it to dry.
Please don't hesitate to contact me should you have any questions!
James Doran Webb