We got knife blocks with built in sharpeners, they work fine. Every time I pull a knife out I run it through the sharpener a couple times.
This is similar to what we have:
The black rectangular bit on the right side is the sharpener. Or you could just get a simple sharpener and mount it on or near your existing knife block. The point is to have it handy every time you use the knife. It's easier to keep a knife sharp than it is to sharpen a dull knife.
If you always keep it sharp, you don't need anything special. Any of the common sharpeners that have two stones mounted at the right angle, and you just pull the knife through it, will work fine.
My opinions are barely worth the paper they are written on here, but hopefully they can spark some new ideas, or at least a different train of thought