And before there was an Anti-Lander Defense System, there was another method employed by the Martians to hide things from our eyes:[1]

On November 14th 1971 NASA's Mariner 9 became the first spacecraft to successfully orbit another planet.

...

Except what came back ... were not pictures of the intricate canyons, craters, and mountains of Mars, but pictures of a blanketed world, a dust enshrouded mystery. Mariner 9 had arrived in the midst of one of the greatest global storms humans have ever witnessed on Mars.

[1] http://blogs.scientificamerican.com/life-unbounded/the-great...

I was thinking more like parties interested in sabotaging the line of research due to personal vendettas against the scientists who would gain from this success, or those who have ideological reasons to block what may be discovered using the technology. I realize this may be far-fetched conjecture, but I'm just sharing my thoughts.