Duradharsah means He who cannot be overcome by others and especially demons and non-devotees can never approach or overcome Him.
Adharsha means to be vanquished. So Duraadharshah means the Lord is Invincible. There are several instances in both Mahabharata as well as Ramayana to clearly show that the Lord is invincible and the Daitya/demons can never vanquish Him. As little Baby Krishna, He snuffed out the life of the demon Putana, Shakatasura demon in the form of the cart, Aghasura and so on. He personally vanquished several of the demons proving He is all invincible. As Lord Rama, He vanquished the mighty demon Ravana with His transcendental bow. Lord Krishna and all His weapons are also equally invincible.
But this same Lord whom the demons can never touch because of their pride, arrogance and hatred towards the Supreme Lord, is easily captured and embraced by Pure Love from His devotees. There are several instances of how Pure and True Love and Bhakti has won over the Lord.
Lets chant the Holy Name of this invincible Lord and pray that we become invincible to the effects of Maya and remain strong always in the path of Bhakti. Nama 82 – VishnuSahasranama