Upgrade to HQ14. Get 2nd Boom Cannon. Defending Tanks will be a bit easier then.
A good way to discourage flanking is to place Boom Mines on the paths where they would flank (this will usually be the edges of the island)
Also, place cannons and booms just behind normal buildings. This way it takes slightly longer for the tanks to take aim at them. Make sure they are far enough apart so they cannot be shocked with a single shock. You can use trees to hide some defenses to fool people as well. Check the attacks when you are defeated and try to adjust your base to prevent repeats of the same attack. Good luck! Ps Blue statues of course help a lot as well, but i rather like to invest in red and purple
I tried a beach base and it worked out perfectly. Killed TWO tanks during a defense.Â