Bronze buckler got super nerfed and is no longer the endgame shield. Keep your shield tier up to date and don't use a buckler beyond the swamp. Trolls are especially heavy hitters and only a parry or dodge will work.

Check the wiki for skill XP. XP is per block+parry, but it takes hours to grind even a moderate level with it. Better shields cost less stamina, and parry costs a lot of stamina. The ideal is to get rapidly attacked with a tough shield and weak enemies. Maybe the elder boss(or 5) would be good for shield practice...