I have never heard of the verb "dug", which means it almost certainly does not exist.

Gena has answered your question very well. The verb "dug" only exists as the past tense and past participle of the verb "dig". The noun "dug" exists independently, but that's another story.

Present is: I dig, she digs Past: I dug Future: I will dig I have dug, I would have dug I will dig, she will dig, I will have dug Any way you say it the word is dig or dug