Uncapped T-posts.

Impalement is never pretty.

This horse was lucky ... he'll live, and probably make a decent recovery.

Horses impaled through the chest when panicked and attempting to jump ... not so lucky.

T-post caps were made for the purpose of protecting your horse from impalement. Use them. Better yet, are T-post sleeves.

Better than both ... wooden posts. More expensive to install, and worth it.