What steps have been taken to rule out instrument failure due to blocked static ports or pitot tubes? In the case of Aeroperu Flight 603, a fatal crash was caused by duct tape that was accidentally left over some or all of the static ports on the underside of the fuselage after the aircraft was cleaned. As the static ports are critical to the operation of virtually all of those flight instruments that provide aerodynamic data regarding airspeed, altitude and vertical speed to the pilots and to the aircraft's computers, this bit of duct-tape caused the total failure of multiple basic flight instruments.

Another crash was caused for a similar reason: pitot tubes that were blocked by an insect led to flight instrument failure, and later, a tragic crash. This was Birgenair Flight 301.

These accidents happened in the mid-1990s. Today, two decades on, are there better systems in place to ensure that static ports or pitot tubes don't get blocked, causing instrument failure?

Edit 1: In both these flights, the pre takeoff checks missed out on the blocked static ports/pitot tubes. Human error clearly happened at this stage. Question is, have an steps been taken to make the flight instruments proof to this particular human error?
The best thing way to mitigate an issue like this is to draw attention to during the preflight check. Its becoming common to use covers that have a nice big red "Remove Before Flight" tag on them. These should be used as much as is practically possible (storage, cleaning, maintenance etc.)  

Something like this would do nicely. 

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Similarly the aircrafts paint may be done in such a way to make the port stand out. 


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Caps/Covers for both static ports and Pitot Tubes are generally a good idea and can help prevent a clog that occurs while the plane is on the ground. As with anything diligence during preflight is key to avoiding this issue. 

Most larger aircraft pilots call out "airspeed alive" during their takeoff roll as a way of confirming the Pitot system is working. If the air speed indicator does not read, the general procedure is to abort the takeoff. 

Some aircraft may also be equipped with a radar altimeter which can help mitigate serious issues by providing an altitude system not based on the static system. However this only works at lower altitudes.