sure there are products that exist, however they are either impractical or you have already said you are not interested in them. therefore, you're just about limited to what i said above unless you decide to give a little.
also, your question was "how do i prevent my keyboard from getting dirty" not "what keyboards are easier to clean" and my post above clearly answers the one you asked. and it should be known that even keyboards which are washable will still get dirty and need cleaning - there is no stopping the cleaning process but there are models which are certainly easier to clean than others (but that was not your question).
-there are washable keyboards: you refuse to pay the price for them, want wireless and think they are ugly. besides that, some have quite a bit of input lag. there are wireless versions but they cost even more and have the same bugs.
-there are silicone keyboards which roll up: they are spill proof, waterproof, washable, etc. the problem is that they are horrible to actually use and feel like typing on gummy bears and are still wired.
-there are laser keyboards, however you want a real keyboard not a sensor.
- there are some keyboard covers on the market, however they are only for very specific models (often for chic-let style keyboards: apple has alot of them). covers for full size keyboards are not common anymore so you might have a hard time finding them for many products since designs for button layouts differ. dell has some, but you're then limited to a what they have. as far as actual use with them... they are very strange to use and chances are you will not like it.
-removable keys. yes, certainly an option and cherry keys are easily removed however you already stated you did not like to take the keys off which made this a non-solution. also, that does not prevent dirt from getting into the keyboard.