He's an old fox in the industry; nobody can fool him.
あの政治家はまさに古狸だ。
That politician is a real old hand.
Standard kanji spelling.
Mixed kana-kanji spelling; less common but still encountered.
Compound of 古 (old) and 狸 (raccoon dog, badger). In Japanese folklore, badgers (or raccoon dogs) are tricksters, so an old one is especially cunning.