For a while now I've been making good use of the "eyes in the back of my head" scenario. It's an oldie but a goodie. Alex is quite convinced of its veracity, largely because I have used tricks such as turning my back to him and reporting on his actions by watching his reflection in our glass doors. When he wants me to close my eyes he now instructs me to close my front eyes and my back eyes. It's worked a treat.
Like any lie, it is in danger of coming unstuck due to the complicated web of clauses and sub-clauses I have employed. For instance, my back eyes can't open while I'm driving, because it's too distracting for my front eyes - which is how I got around the "look at me mum"..."I can't I'm driving"..."use your back eyes!" Also, dads don't have back eyes, only front ones (which, ahem, even then don't always seem to work). So Alex played along and 'stole' my back eyes to give them to dad.
Because of the pretend 'back eye stealing' I started to suspect that the technique was starting to lose its sheen, then recently it came into its own again, however I had to employ slightly new logic. I was riding my bike home from a friend's place with the kids in the trailer. I heard a kerfuffle but couldn't turn around and it died down soon enough so I didn't stop the bike. When we got home, though, on taking Maya out of the trailer I noticed two big bite marks on her arm. Normally Alex is not a biter but recently Maya has been testing out her chompers so I'm sure he was doing the whole get-you-at-your-own-game thing. No excuse, obviously, and he had to be confronted. Surprisingly, instead of using the 'she did it first' line of defence, he went straight for the completely implausible 'it wasn't me'.
Me: "OK who was it?"
Alex: "It was Maya."
Me: "You're trying to tell me Maya bit herself on a part of her arm she would not even be able to reach?"
Alex: (butter wouldn't melt): "Yes."
Me (changing tack): "Well I know it was you because I saw it with my back eyes."
Alex: "But you had your helmet on!"
Me: "Well they moved down a bit to just above my neck because of the helmet." (I indicated the spot).
Alex: "..." (hangs head, busted).
Me (in my mind): Check mate.
Me: (out loud): "Well now we've established that it was you, you need to apologise to Maya."
Alex: "Sorry Maya."
Luckily he didn't think to challenge the ruling using the precedent of 'no back eyes working while driving' because technically we were on a bike, but I'm not sure how I would have finagled that one. Considering he's only 3 I can't wait when he's old enough to really argue the point...! I have no idea where he gets it from.