Copper Aluminum Ground Connection - Code Question

There are wire terminals designed for use with both copper and aluminum. They will be marked "CU/AL." You could also use an antioxidant compound such as "Noalox" or "Penetrox."

As for the code question, the National Electrical Code (NEC - I'm referring to the 2005 version here, but I don't think this has changed in more recent versions) talks generally about connecting dissimilar metals in 110.14. Check your NEC's index under "Metals, dissimilar" for additional specific references.

NEC 600.6 addresses protection against corrosion and deterioration. Sounds like you simply need a electrically conductive, corrosion-resistant compound unless you are using stainless steel (in which case you don't need it). Otherwise, this stuff comes in a small tube and is available at any sizable electric supply store.

since i suspect that the termination is exposed to the elements and you are in a coastal area, i feel that using any corrosion inhibiting grease will have limited life.

please instead use a CUPAL washer at the interface and use brass or stainless steel fasteners. also try to shroud the connection from direct splashing as much as possible.

the code references of NEC are already given in other answers.