Q.Something is eating the leaves on my avocado plant. What can I put on it to keep the critters off?
What can I put on my plant to keep whatever it is from eating the leaves?

From the photo, the holes in the older leaf and the chewed leaf margins appears to be from a caterpillar or snails. Was the plant outside previously where it could have been exposed. If so, maybe the problem is no longer a factor.
Try to identify what the pest is. On a small plant you can sometimes pick off a pest, or take it outside or in the bathtub and wash it off, and not have to spray.
Neem oil is a preventive repellent for insect pests but may not affect snails.
https://www.domyown.com/monterey-70-neem-oil-p-2841.html