If I actually had to boil it down for that model feet on wet sidewalks go for a true extra that model box and a rubber outsole with grooves that move water. Keep the shoe light so he does not tire out and avoid overly squishy foam underfoot. Try them on late afternoon and walk a few steps on a damp area while holding a rail, you will know right away if the grip feels secure. Replace them when the tread looks shiny or flat since that is when slips start happening.
