Get a lead ladle and a pot to melt your lead, a real cast iron one is best. Now get a shallow box of slightly damp compressed fine sand, just damp enough to hold a shape.
use your ladle to make an impression into the sand of the ladle bottom, as many "molds" as your box will hold but don't over crowd it. A ladle about 2 1/2" across will make a mold for a finished anchor of 6 to 8 oz.
Now take some copper ground wire and cut to size, this will depend on if you want to fit the ensuing "hoop" to fit over the decoys head. when you have your "hoop" set, bend about 1/2" of the ends to make little "feet", (make sure the hoop will still fit over the head). These will be covered by the lead and hold the hoop in place permanently, shape your hoops on the bottom to fit your molds or ladle.
Now, melt your lead, take a ladle full and pour into your sand mold while holding the hoop in place, use a pliers. Hold for a few moments until the lead hardens around the hoop. When all your molds are full, and the lead is cool, remove from your mold box, if you want to make another batch, you need to re-compress the sand and make new molds.
Alternatively, use a muffin tin, just be careful to not make your anchors too heavy by filling the holes too much, or.... make one anchor at a time by filling your ladle with melted lead and hold the hoop right into the ladle, let cool a few seconds and dump out.
Don't make your sand too damp, and don't breath the fumes of the melting lead. Use gloves and eye protection, wear long sleeved clothes, nothing fleece or synthetic, don't do this barefoot, lol Be careful, make sure you have nothing to trip over around your work site, and your molds, pot, etc are stable.
You may want to check the weight of the first one made so you know how much lead to pour, try and keep them consistent
This style works very well in tidal areas, if you just need a weight, it's pretty hard to beat a cheap Banks sinker.