Hi - this may be an unusual request but I do some volunteer work for a local fire department here in suburban ny. They are putting together a memorial plaque for their quick rescue team. They need the following quote tranlated into Gaelic..."No fucking slack"...I apologize for the profanity but that's waht they want...I appreciate your help.
Maire Brosnan

A Mháire, a chara,

I would advise the simple phrase :

Teannaidh oraibh!

Which turns out close to an urgent : 'Tighten up guys!

Sounding as : Tchanee urive

or as : Tchanee uree.

That gives you four syllables and I would advise not going further.

If, however, you are not worried about length, then the profanity which intensifies the urgency in English could be inserted again in Irish, strangely, by adding 'for God's sake' = 'as ucht Dé.

Sounding as three syllables : os uchkt Jay,
or as two syllables : 'suchkt Jay

Teannaidh oraibh as ucht Dé

or :

Teannaidh oraibh!