I have an older deck that is weather treated wood that has been painted with regular latex exterior paint. I have two kids and four dogs and have not been able to find paint that with last even throughout the summer without completely chipping and flaking down to the bare wood surface. Is there a hard enamel or polymer finish I could use that would last longer and if so where would I get it?
Umm, no paint in my 40 years of experience will last on wood under foot.
Your question regarding a hard enamel is, though serious, looking in the wrong direction. Due to the constant change in moisture content, vastly differing temperatures and the grit from the dirt on shoes and such, a floor paint will just not hold up on wood.
I will always recommend a semi-transparent deck stain for wooden decks…. except in your case. Stains are not appropriate over a previously painted surface.
Choices? Replace with new boards and stain. Allow all the paint to wear off and stain. Pressure wash as much paint off and stain. Keep painting each summer and move on to other projects.