The Dogecoin Development Team, in an effort to boost the hashrate and prevent a future 51% attack, will soon be implementing merge-mining capabilities with Litecoin. To implement this, Dogecoin will be transitioning from its current proof-of-work algorithm to an auxiliary proof-of-work algorithm.
The auxiliary proof-of-work algorithm will enable any scrypt coin with a higher difficulty than that of Dogecoin to send work to the Dogecoin blockchain. As Litecoin is currently the only coin that fulfills these two requirements, it will be the only coin capable of being merge-mined with Dogecoin; at least at the beginning. The switch from proof-of-work to auxiliary proof-of-work will require a hard fork of the Dogecoin blockchain.
According to a core developer, using the Reddit username langer_hans, the switch from PoW to AuxPoW will come “sooner than later.” In his announcement, he notes that the feature is in a “late-testing phase,” and notes that it will still be possible to mine Dogecoin independently of any other coin.