The Brahmasthra to proctect ourselves from evil people or evil forces is doing any Prathyangira sadhana.
Prathyangira devi is the godess as her name suggests Prathi-Manthra-Bhakshini, Prathi-Paksha-Dhvamsini.
She is one of the five vidhyas of Pancha-Kaalika Sampradaaya of Shaaktheya Tantra.
She will grow stronger as the enemy uses stronger powers against us.
Some people mis-understand that she is a Kshudra Devatha. But she isn't.
Actually Pranthyangira Sadhana is derived from Atharva Veda which contains the Rukhs(Atharva Veda Verses) of godess Prathyangira. Angirasa Maharshi is the Drasta( who gains the experience of the god in his meditation and provides us that experience in the form of Vedic Verces) as the name of the godess goes Prathyangira.
There are as many as 64 rukhs about Prathyangira in Atharva Veda.
There are also different types of Prathyangira vidyas like Angira, Upangira etc.
There is a proverb in Telugu language about Prathyangira Vidhya; "Prathyangira chesevaadi panchanaki vellaradu, Upangira chesevaadi oolloki vellaradu". It means "Don't ever go to the side of Prathyangira Sadhaka and Don't ever go to the village of Upangira Sadhaka", This is because the sadhakaas of these vidhyas are "Nigrahanugraha Samardhas" as they can give Vara and they can thrash shaapa.
If we observe the history the maharshis Vasista, Gauthama and Angirasa are the Uapasakaas of this vidhya. The shankha of the god Shani is called Prathyangira. This is because Shani is the upasaka of Prathyangira and she gave her anugraha as she will be present in the form of his shankha. So there will be no effect of shani on the sadhakaas of Prathyangira.
Meghanaatha the eldest son of Dashakanta was worshipped the Prathyangira in the form of Nikhunbhila( means never allows the enemy to breathe) and using this vidhya he beat the Indra and was gained the name Indrajit. If we observe Raamayana, even avathaara purushas like Rama, Lakshmana and Hanuman were unable to stop Meghanaatha in Yudha. But Vibhishana after revealing about the sakthi of Meghanaatha gained by perfoming Nikhumbhila Homa, Hanuman destroyed the Home on the day he was killed by Bramhasthra by Lakshmana. This is the sakthi gainined by doing worship of Prathyangira.
I m planning to present you the 64 vedic verces of Prathyangira and their translation into English for you people, which will be very useful for us.
I m also planning to present you "The Thrailokya Vijaya Prathyangira Kavacha" and "The Jaganmangala Namaka Prathyangira Kavacha"
For the mantras of Prathyangira please ask our respected Dhruv Ji as I m not eligible to reveal mantras because I m still a shishya.
For now I m urging all the respected members to do sadhanas of godess Prathyangira to not only protect theirselves from Bahir Shathus( Enemies those are out in the world) but also from more stronger Anthar Shathrus in the form of Arishadvarga( i.e, kama, Krodha, Lobha, Moha, Mada and Mathsara).