Research on here for that problem and you will find many ideas used to slow him down. Use the search tab at the top and put in the problem and you should find threads or post on this problem. My favorite way to slow them down is to put his meal in an interactive toy so he has to work for it and the food comes out slow so he has to slow down eating. Do keep in mind that dogs that gulp their food are more pron to a condition called "bloat" so you do want to get him slowed down.
This is what we use with Koda. She inhaled her food as well and our dog sitter recommended this to us. It is AWESOME! Keeps Koda occupied for about 10-15 minutes depending on how long the last piece takes and keeps her from inhaling it as well!