For walking the dog, and generally bimbling around, some ex-army combat trousers, with whatever pattern takes your fancy. I was lucky enough to grab a couple of pairs of Danish Army trousers when they changed to Multicam, like the British Army, and put all their three-colour Flektarn on the open market. Two pairs of combats and a field jacket cost me £70, previously that’s what one pair of trousers cost.
What makes them so good is that they’re 3/4 lined, so a lot warmer in colder weather, and really comfortable to wear, they don’t soak through as quick in damp conditions. Also, mud doesn’t show so much, which if a dog is jumping up at you, does make a difference.
There’s probably loads of German Army flektarn stuff around, I think they use moleskin for their kit, and again it doesn’t show the dirt, also, combat gear has lots of handy pockets for things like leads, poo bags, etc.