Q. How can I get two guinea pigs to get along?
A. Pairing Males
There are many schools of thought on this very topic. One is if your guinea pig has been alone all this time then he isn't going to know anything different as long as you are spending lots of time with your fellow. If you are not spending time with your guinea pig then letting that fellow pick a new companion would be the next step. Someone around his own age, some one slightly younger but not a baby. Putting an adult this age with a baby is like giving your grandfather a baby to care for and compatibility is rare.
Being able to let him meet on neutral territory with the creature would be ideal and offering him several choices of companions, is a place to start. Watching their posture when interacting is important and it is important to remember that they will play out this same dance again when you get home. It may even become more animated and aggressive and owners who have an additional cage available would be truly ready for this experience.
Guinea pig posturing what it means on the first meeting:
1. First they will greet, trying to smell under the chin and then smelling the bottom. This means do you trust me or are friendly if the receiver permits the behavior...smelling the bottom means I know your rank in the herd
2. Then they will move about each other smelling and reenacting the behavior in number one. They may add purr and rumbling and/or teeth rattling to this as they do so. If they are compatible right off the bat, one will gently lick the others eye or ear flap and they may even lay down together or act completely uninterested in the other..
3. Males will mount males, females-females as a way of saying literally "I will be the top guinea pig in this relationship." Just like in human couples there is always one individual who is the front person and one the support. It is the same for guinea pigs. If one allows the other to mount and not take it to step four then you can be fairly comfortable they are a fairly match.
4. Guinea pigs will rattle their teeth, this is called shaking their sabers. Minor teeth rattling is OK. Major teeth rattling is not. If a guinea pig yawns then that means see I have huge teeth and can hurt you. Then a guinea pig will move to striking with their teeth like a head butt to indicate that you are not getting the better of me and than finally when they head butt but come back with hair in their mouth that means the next strike will be a bite. Separate them immediately. This is a pairing that is not going to work.
Now with males this can be a pair that will get along today, tomorrow, a week a month and then for no apparent reason have a falling out, something is said and they will never go back together again. Any kind of fighting especially rolling around in the shavings is an indication that they are not compatible and should not be living together. Guinea pigs will fight to the death and there are many who do not want a companion. They don't mind sharing floor time but they can not share the same cage.
So with this knowledge and knowing your guinea pig only as you do can you make the decision of what is best for YOUR guinea pig.