the only problem with taktik's hold for me is that reaching over with the left arm will wear that arm out after a while!
One of my favorite things to do is to use a PILLOW as a distracting weapon!!! I've done this with a lot of friends because wherever you go, USUALLY, most couches have arm pillows within easy reach.
What you do is take the pillow in ONE hand (grab in the middle where you have full control) and shove it in their face! NO, NOT TO ASPHYXIATE!!!! But aim for the forehead, under the chin, or sides of the face. Guaranteed they'll try and remove the pillow distraction with both hands because let's face it. It's annoying to have things in your face, blocking your view...etc. While their hands are trying to remove the pillow, just tickle away with your free hand! The minute they try and stop you from tickling, just refocus on using the pillow as a facial distractor. It's amazing because the priority for them will ALWAYS be on getting that DAMN pillow out of their face, and you don't have to expend a lot of energy or strenuous positions trying to hold them down! It has never failed, no one's ever complained. Seems visibility is the biggest thing because they want to see where you're trying to tickle them, and if they can't see it, they can't block it properly.