I use glass blocks. Rather than keeping them from glitching through, it doesn't kill them when they eventually do. I have also heard of people using glass blocks, and then using water streams aimed at the enclosure. If they do glitch through, the animals should be pushed back towards the enclosure so that they at least can't escape.
ah water is a good idea, i'll figure out how to make that work for me i just checked earlier and out of 100 total entities on my res, 24 of them had glitched through some wood so i couldn't see them. i had to go through and break down the entire structure and then they all started appearing. luckily none of them died or seemingly took any damage.
/res set animaldamage false (may already be default, not sure) Then use wheat or seeds or carrots to lure them out of the walls and into the center of the pen. With animal damage false, you can then use solid blocks, which helps. I always use at least 2 blocks thick on EMC so they do not glitch out. Hope this helps.
