Rabbits reach “puberty” when they are between 4-6 months old. This is when their hormones kick in, they tend to become more territorial which leads to marking. Sterilizing not only prevents unwanted pregnancies and decreases their chances of reproductive cancers, but also calms them, improves their behavior, and increases the chances of them using a litter box. There are no behavioral changes in sterilizing a cavy.
Rabbits and cavies like to do their business while they eat! That means having a litter box big enough to contain all their hay, still allow for a clean space to defecate, and even large enough to take a snooze in, is ideal!
Step up XL litter box with 2-3 inches of safe litter (such as pine pellets, paper pellets, aspen shavings, or unscented paper bedding... no clumping litter!)
Place their hay feeder above and/or in the box (we prefer to use hay bags, but you can also just stick a pile of hay down for them too!)
Place the litter box in a corner of their enclosure (if your rabbit already has a preferred part of their enclosure, start there!) (for cavies, we suggest having this part of their enclosure covered)
Limit their free roam time until they become accustomed to using the litter box regularly (this will prevent them for continuing to poop outside of their enclosure)
When free roaming, we suggest adding an additional litter box outside of their enclosure if needed.
Always ensure they have fresh hay! It will need to be replenished multiple times a day, especially since they are likely digging through the hay and peeing on it.
Dump the litter, wipe down the box, and refill when it gets full (suggested every 3-4 days... if the box gets overly full, it may cause them to go outside the box).
With any training, it takes time! But sometimes when rabbits are pooping outside their box, this can be due to feeling territorial. It is a rabbit's way of marking their territory. We suggest scooping up their poops and placing it inside their box so they can see where it goes. But sometimes, this behavior does not completely stop.
Cavies cannot control their bowel/bladder and likely will never be 100% box trained but offering a box does help contain the mess.