Re: Auxiliary verbs

I've been thinking of that option for my conlang as well. Just to give an
example:

<i>Sakuneg shirenegrel</i>: you (pl.) must go to the west (where 'sakuneg'
is the lative form of 'sakon' (the west): to the west; shir- is the personal
pronoun for 'you' (plural); en- is the verb stem of 'eno': to go; -egr- is
the modal infix 'must' (mandatory, obligatory) and -el the suffix of 2nd
person plural present tense.);

<i>Sakuneg shren enegrel</i>: you don't have to go to the west (negation
accomplished by negating the personal pronoun 'shir' to 'shre(n)');

<i>Sakuneg shirenendegrel</i>: you must not go to the west (with -en(d)-
inserted between the verb stem en- and the modal infix -egr- to indicate a
negation of the verb stem).

Still, I wonder whether this is the best solution - therefore my question
how other languages tackle this 'problem'.