I am sure this is what your pastor means.... Its rocky.
But in all seriousness I love the advice you have been given thus far. I would definitely go and speak to your pastor and be honest. Tell him you want to honor his request, but you aren't sure what he is looking for when he says "rocky" If you can get him to explain it better and maybe give examples then you can give him what he wants or at least get closer.
When I think of rock, I think of memorable riffs on the guitar, driving bass, stong drums, and a powerful vocal. You don't need electric specifically, as has been mentioned, but that might be what your pastor is looking for. So it is best just to ask him and let him help find the sound he is looking for.
I would definitely agree with continuing the discussion regarding what style (specifically) your pastor is looking for...if there are others from your church who have also attended some of the same conferences, consider asking them to describe the music as well.
Also, you did mention a keyboard player...if it's a keyboard (not a piano, etc.), spend some time experimenting with different settings on the keys, as well as different patterns (chords instead of scores, percussion patterns, etc.).
More cowbell... awesome reference
This is pretty subjective but I would consider a bit of change in the mix with more drums and electric guitar over the congo and acoustic. But the "have him find some youtube video" is also a great idea. A lot can change based on voice as well, for example, I don't have a "rock" voice therefore my voice in that mix wouldn't sound as "rocky" as others.