I can understand why he wants to escape, that cage is way too small for an adult bearded dragon. Three feet long and one foot high (unless your width is 3' or more) is much too small. The minimum size for an adult dragon is 4'long by 2' wide by 2' high.
Not sure how you have his basking light and UVB light set up, if they are suspended above the cage or laying ontop of the cage lid, but with a foot of height and your dragon is able to jump that high to get out really puts him at risk at brushing against his hot basking light and burning himself. If neither light is firmly attached, the dragon could also accidently knock it off the tank and cause a fire hazard.
My suggestion, build or buy a larger cage, with at least 8' square of floor space (4x2, 3x3, 3x2.5' etc) or more. Also, increase the height to a minimum of 16" this way there is less chance of your dragon jumping high enough to escape or burn himself on the lights. I am sure once you have a larger cage for him, he won't feel such a need to get out. My dragon was in a 5'x2'x2' built cage, she loved it. she was always running around the length of the cage, very active. The only time she would scratch the sides was when she pooed and wanted me to get up and clean up after her, or if I was sleeping in on the couch and she wanted me to get up to feed her. Sometimes I think she just wanted me up..as once I was up, she would go climb her basking log and act like nothing had happened.
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PHLdyPayne