Thanks everyone for the compliments and helpful suggestions.
Maybe I can add a few rain/dirt streaks and mud splatters to the halftrack and a little dirt pigment/ mud splatter to the figs.
I used my same sidewalk weed preventer "polymeric sand" that hardens solid in a day or two with simply spraying water on it. While it was still moist I fitted the vehicles and figures and churned the mud around the track areas. Also before completely dry, I used snow-cote to soak-in/mix-in with the mud (painted with oils). After dry, I added more snow-coat over the damp areas for the snow patches.
I've used the polymeric sand with all my dios so far (desert, woods, snow, whatever) and it works good for a dio beginner like me and your wife will be happy how there's no weeds in your driveway