Caulk, or a piece of asphalt shingle works just as well. The old timers used horse poo, which I happen to have in abundance, and I can attest that it works well also.
It's a well used Peter Wright, good old anvil.
One of the best things Peter Ross (Colonial Williamsburg) taught me was that you don't need sharp corners on an anvil- forging isn't about stuff like that, you put that in later.
I do require a good flat, true face, though, and that one looks fine.
It's always good to check new anvil prices in case someone tries to tell you that old anvils are better and charges you more- they're not better, the new cast ones are quite superior, but the old ones work great also.
Not all good anvils ring, but a wrought/hardfaced anvil that doesn't is probably junk.