Is there any technical reason that prevents installation of a jet blast deflector at Princess Juliana airport?
An immobile jet blast deflector could not be built far enough away from the runway end to be safely clear of the landing path. Large airplanes like 747s must touch down pretty close to the near end of the runway, which is right at the edge of the  beach, a blast deflector would be a serious hazard if an airplane came in a bit too low. Here's what I'm talking about:


A static deflector would be extremely close to the path of the landing gear. 

It could theoretically be possible to install a retractable one, however sand does not make a good building surface and therefore it would be real engineering challenge. 

It seems much more likely that the authorities, if they do anything, will install more fencing or other barriers to deter people from getting so close rather than install a blast deflector. This would be cheaper and achieve the same effect.