Your Atlanta home has a really nice stained wood front door whose clear coat is deteriorating and the stain is fading. More than likely what you have is a door that was stained with a typical interior wood stain and then coated with a polyurethane clear coat. If there is no overhang or the door gets a lot of sun it probably only took a year to degrade. If this describes your situation you should directly to step 3 because you are going to end up there anyway. If your door lasted several years you should consider preserving the wood finish a try option or 1 or 2.
Option 1- If the door is only slightly damaged you can light sand (barely touch it as you are not trying to remove the poly) with fine sandpaper and coat with two coats of poly. Repeat annually until you are forced to step 2.
Option 2- If the color is badly faded sand all the poly off , stain it and apply two or three coats of poly. The door surface is probably just a thin veneer of nice wood over cheap wood. If you sand to much you are going to get down to the base wood. Coat annually with poly.
Option 3- Prime the door with an oil based primer and add 2 coats of paint. You probably do not want to lose the natural wood look but you don’t want to refinish the door every year or two either. This will stand up to the weather and will save the door from the junk pile.
You want to preserve you deck or fence. DO NOT PAINT IT. Stain it.
Preparation. If you have a new deck let it acclimate for a few weeks in the summer or for a few months during the colder months. If your deck was already stained but is no longer beading water prep it with 10% bleach solution, pressure wash, and let dry. If the wood is still beading drops of water when wet then use a stripper before doing the above.
Staining. Never use a transparent stain. Sun does as much damage to wood as water. Choose an exterior semitransparent or solid stain. The pigment in the stain is what protects the wood from the sun. Two coats of the solid will look great. Two coats of the semi will look a little blotchy with some wood showing through. Three coats of the semi will look just like 2 coats of the solid but is a much stronger finish because it penetrates the wood.
Staining the bottom of the deck- You can do it for cosmetic reasons but is not really needed. The top surface (no matter how well it has been cared for) is always going to call for deck replacement long before the bottom. There is really no point in sealing the bottom to last 100 years when the top is only going to last 30.