B.R.
Try a FIRM, "No". Try not to look surprised, or shocked. Immediately after you say, "No"...take him away from your breast and stop the feeding. My baby did it at like 4 months and then never again. My mom said the same thing happened with me, she did just what I told you, to me...I never did it again either! After 1 year, I am under the impression the child gets no more nutritional benefits from nursing. Maybe you should take the feedings to nightime only.
My great grandma nursed one of her boys till he was 4. She was having a tea party one day, and he walked in, pulled up her shirt, and latched right on. I say, when they are old enough to tell ya what they want...well, they are old enough to drink from a sippy...hahahaha.
It may be easier to stop now then when he is 2, and he is going through the "TERRIBLE TWO'S". They are not as easy to reckin with when they get that 2 year old mentality.
Good luck