HDHM polyethelene. The acronymm is High Density, High Molecular weight. Sheets of it are used to line the chutes for ore dumping facilities, and to protect the edge of highway snowplows.
I used to make dog sleds out of it. 1/4" outlasted oak runners by about 4:1 Can be machined with wood working equipment. Cost is about $1-$2/pound. Ask at industrial plastics stores. Sometimes you can get scraps for cheap.
Downsides: you can't glue it. You can screw it. I would suggest using a layer of slow set epoxy putty as a void filler, and screw with large head short screws. You need to counter sink the screw.
The material is available in thicker chunks. You may be able to replace the whole skeg with PE. Be a lot easier and not much heavier.