Time for another round of pin the tail on the donkey...
“Sleek looking” narrows it down. I’m with mcglouhlin on this one = Bynoe’s Gecko (Heternotia binoei) They have a tail shape more akin to that of a skink than a gecko and a slender built. They are also the variably patterned and coloured gecko I know. They are probably the most common gecko found under surface debris, especially sheets of metal. Google some pics but keep looking until you find one with irregular white dots.
An under nourished Oedura monilis or O. tryoni might also fit your description. However they are primarily rock dwellers, also sheltering under bark. I personally would not describe their dorso-ventrally depressed bodies as “sleek”. ANG can be dark grey but if they are patterned, they have pale flecks or splotches, rather than white spots. They also tend to a definite pattern of dark lines down the body – something you would notice straight away.
Blue
PS. What do you a dinosaur that is about to attack you?... “I-think-he-saurus”.