It finds a cave or abandoned building and seals any doors, windows, openings or cracks with a concrete it produces by mixing it's dung and urine with dirt and straw. The inclusion of it's dung insures that the mixture, once it's dry, will be nearly indestructible.

Within days the creature's hideaway, built out of shit and dirt and grass and supplied against the coming freeze with eight or ten
decaying corpses shoved into a corner and growing more and more "cured" by the day becomes rather close and, in fact, develops a stench that is legend on a dozen worlds.

The stench is only one way that the bull appears to discourage visitors during it's "rut". The isolated location of the enclosure, it's network of pitfalls, sharpened stakes and tripwires, it's reputation and, most of all, it's ferocious and deadly occupant ensures that the occasional hiker or game warden who stumbles upon the vile abode of the Bull Nephilim turns and flees without hesitation
usually emmiting various screams, curses and exclaimations as he goes...but not all...

And then there is The Weapon, the Nephilim's incredibly ancient and frighteningly powerful weapon,...