There are many synonyms that can be used for the phrase "march against," depending on the context and intention of the protest. Some of the most common synonyms include "demonstrate against," "rally against," "protest against," "stand against," "oppose," "resist," and "protest." Each of these words conveys a similar message, but with a slightly different tone or nuance. For example, "oppose" and "resist" may imply a more forceful resistance, while "protest" and "demonstrate against" are generally more peaceful acts of dissent. Choosing the most appropriate synonym will depend on the situation and message that the protesters want to convey.