Hello @afre
Are you intending to sharpen the unfocused areas so that they are more alike the more focused ones?
Nope, my note about the tail not being completely in focus was just a casual remark.
Actually, I took many pictures of this lizard and one of them it appears most suited to make some experiment about sharpening.
Here it is (jpeg very compressed to post here):
Here is the NEF file (Nikon D700) in case you are interested:
BTW, let me ask you a question since you are extremely knowledgeable about G’MIC 
Can you suggest some unusual G’MIC filter in this domain to try in order to sharpen these pictures of mine?
At present, there are tons of them for this particular purpose, with little documentation, shipped with G’MIC and I am a bit lost…