Get yourself about a four foot piece of cold rolled steel bar(round), i think mine is 5/8 diameter. Get ten or twenty wide washers of the appropriate inside diameter and weld on about a foot from the bottom, this is your stop. Weld another piece of rod onto the bottom in the diameter you want, 1/4" 3/16" etc etc. I used 1/4" cuz some of my decoys are on 1/4" alum, and some are on 3/16" steel and the bigger hole seems to work just fine on the smaller stakes.
Now get a piece of steel pipe that will fit over the 5/8 rod. You now have a slide hammer and they work great. You can weld some metal to this pipe to make it heavier if you want.
Works fast, you can stand up straight while you do it ( I usually have someone come right behind me and drop a decoy in the hole, this way you dont lose holes in the dark).
Oh yeah, if you look in the right places the cost is about 1.25 for the welding rods. the rest can be had for free usually.