i havent hunted on public land with cows but on our farm i run into them when i'm on my way to the stand. i just walk straight through our herd and even push them out of the way. you just have to read their body language. if they're head is down and they're feet are spread apart, get the heck out of there. if they are kinda like mean looking anyhow, get away. if you have too, just raise your gun/bow over your head and kind of wave it around and they should leave. just be carefull.