Elbereth

Elbereth is a goddess worshipped by elves. Engraving her name on a square prevents most monsters from attacking you while you are on that square. Engraving the E-word, as Elbereth is often referred to, is also a popular way to protect stashes. Note that there must be something, like you or a scroll, in the same square with Elbereth for it to work. No monster represented by an @ will respect the word, neither do any A, minotaurs or the Riders.

Elbereth stops working when it degrades into a different word. If you are writing in the dust ([E] [-]), you might want to write it several times. The immediate result of one test was "ElberLth ElbereGh ElVereth Ylbereth Elbeheth Elb;reth Elbereth Elbereth tlbere#h".

Engrave Elbereth quickly

A fast method (writing in the dust or using a wand) is almost always preferable over a slow one (actually engraving). Thus it is normally better to write with your fingers (fast, but in the dust) than with a hard gem (slow).

This is because the slow methods give monsters time to kill you. This is a problem both when you need "Elbereth" quickly or if a monster surprises you. Note that characters reading a spellbook or eating a food ration will stop when approached by a hostile monsters, but characters busy engraving will insist on continuing the job. Thus any character engraving with a hard gem or other slow method is vulnerable to attacks from monsters.

For a permanent Elbereth, use a wand of fire or wand of lightning, but be careful not to blind yourself with the flash from the latter.