how to add 404 error to deleted products

I dont know if this has a solution or have been posted somewhere else..i just cant find nothing more than stuff about seo urls.
like the title say...i would really like to do this...i dont know how helpful will be this thing for google...but i dont like it for myself.
for example when i go to http://demo.opencart.com/index.php?rout ... labla____1 it's like the going to the product...and i think this is bad because google will index a lot of deleted products. and i think it's the best whem someone comes from google to a product that doesnt exist to get a not found page ...this will be good for google to know too...
I already added in /catalog/controller/error/not_found.php -> Header('HTTP/1.1 404 Not Found');
but i also need to add something to /catalog/controller/common/seo_url.php ...but it's a bit too much for me. Could anyone help me with this? i am using the last version of OC

hey...anyone , have any idea....i need just a starting point!