Vyahruti is the best digbandhan mantra . Everywhere there are demons and bhutas whose very job is to put some obstacles into good karma . Thus while japa these attack from all the ten sides.Sadhak has to protect himself from these ,else his pooja phal is drainedout by these forces.
how does digbandhan work? Narayan panditacharya in his Yogdipika says , every one has a nrasimha agni in his palms. By clapping thrice this agni is lit and intensifies . Then flames of this agni is used to dispel negative forces by clasping middle finger and thumb , the noise generated by clasp , aggravates the flames of this agni and with astra mudra we can drive away the negative forces and sit calmly in japa or sadhana.