You can go the Ultra Cheap
- Buy a bag of Silica Sand, & I say Silica, as said type of sand contains no iron & thus wont bleed rust in the marine environment
, as will some other types.
- Tape of on your steps where you need the non-skid to be
- Lay down a coat of; Paint
, or Epoxy
as an undercoat
- Sprinkle on sand, & wait for undercoat to dry
- Brush off excess/loose sand, & pull off tape
- Roll on 2-3 layers of topcoat
And if you want to get fancy, you could get a Sign Shop to make you some custom masking templates for each tread with whatever pattern or design you desire. Although likely you could use your laser to do the same thing.
Or, if you want to get Trick, & are really good with that laser cutter. As in good enough to use it to inscribe, do designs & art work
, etc. Then use it to put a diamond checkering (or other) pattern into each ladder tread, & re-varnish afterwards.