There are many ways to design a pet fence in the yard and different types of fence posts that can be used. Some homeowners that plan to install a fence near a wooded area may not care about aesthetics as much as someone that is installing a pet fence in the backyard of an HOA community.
If installing a pet fence in wooded areas, consider using angle steel line posts in addition to nature as fence posts. These lighter weight steel posts have an "L" shape that allows it to slide into the ground, particularly in rocky soils. Holes down the length of the posts make attaching fence with self-locking ties easy and do not require ground sleeves like traditional line posts.
If the fence system will be temporary or in wooded areas, consider using angled steel line posts.