Safety is always first. Wear the necessary PPE before digging holes around your property. Now dig a hole for your fence post. The depth of the fence post hole should comply with the general rule of thumb.
The depth should be one third to one half of the actual above the ground line of the post. Example, if you’re building a a six foot high post, your post should be at least 9 foot tall and that the 3 feet will be buried beneath the ground.
The width should be double the diameter of your fence post. Now that you have dug up the ground, provide at least 2 inches to 4 inches of well compacted gravel bedding to allow water to drain away from the fence post material.
Now, depending on your soil type or if you will still continue using gravel specifically pea gravel, fill in around the fence post hole creating a conical shape to prevent frost heave. With the additional soil or pea gravel, compact the backfill material and refill as possible until all filled up.
After this, allow the material to settle and cure before attaching fence rail, panels and chain links.