You have to figure out what motivates him, maybe a squeaky toy or a treat of higher value like string cheese. This will be his reward.
Next, appeal to the terrier by crouching down with your back to him and pretend to dig. When he comes over investigating what you caught... say 'good come Ruger' then treat.
Never say a dogs name in fustration or anger or they'll end up associating their name with negativity.
So make sure you only use his name when your giving praise.