dude, the gar may not be aggressive in a usual sense but its predatory. Silver fish are viewed as food a lot of the time. The Silver Aro is a large, aggressive aro with a fast growth rate. It'll out grow your gar for sure. As to pond size, I'll have to agree with the other posts and say 9'x3' isn't all that big. Too put in perspective, I'm building a 10'x 5' x 5' for a RTCxTSN.
"big ball of light, spits out dinosaurs" - Mac, Primeval New World
"big ball of light, spits out dinosaurs" - Mac, Primeval New World