Pillar in the ground that can support a hammock
Any freestanding hammock post without lateral binding will eventually work loose.

The standard configuration is to use a 6x6x9 wooden beam and sink it three feet into the ground with a footing made from an 80-pound bag of cement. Where I live the only place to get a wooden beam of that size is a sawmill over 50 miles away.

Alternatively you could use a 3" Lally column as a substitute for the beam.