Hiya this is my first thread so PLZ be nice!

My german pointer cross springer spaniel is great at agility, the only thing holding him back from getting a grade 2 is sometimes his attention wanders and he goes off sniffing. I've yelling at him, being nice to him(treats, toys, ect) and ignoring him. One of my friends suggested doing a few obsticals, then praising him, a few obsticals, then praising, ect but now every now and again he runs off course because he's expecting the praise.
Any ideas??????