Are you sure the motor of the rotator actually runs on the 240v mains power? Most of them use low voltage DC fed from the control box. I would hesitate to hang a large-ish yagi onto a brick chimney anyway. An electrical supply shop will sell you a ground rod and clip, usually a steel rod copper plated. They are usually about 1.8m long and 15mm diameter. A surge protector may survive a nearby lightning strike but nothing will protect you against a direct hit.
If you want to see a real lightning protector go to you local church that has a steeple and inspect the solid copper bar running from the top to ground - sometimes more than one. The bar will be 50mm x 25mm and even bigger - that's assuming it hasn't been stolen!