Rottweiler Puppy aggressive

Question
My Rottweiler is 75 days old now. I tried taking him out for a walk on a leash, but he refuses to. He holds the leash in his mouth & never comes for a walk, he sits on the road, unwilling to walk. He gets scared of vehicles, though I manage to walk as per his speed & will, I wait for 20 mins or more, he never pees or poops, as soon as I return back home, he poops inside the house only. Please advice how to make him feel happy taking out for a walk. Thanks in advance.

Answer
Walking on lead is a basic.  Usually getting out in front and coaxing, slapping your thighs is enough.  If that doesn't work, drop behind him and run by in baby steps calling ''Go, go, go!'' in a happy excited voice.  

Getting him moving is the key to the bowel movements.  Walk, walk, walk, they can only walk and hold it so long.  When nature takes its course, lavish praise on him.  I didn't walk 14 week old Xanthe far enough this morning before going in Home Depot. Sure enough, she had a bowel movement.