Sobre la marcha, “on the march.” The Diccionario del español de México of El Colegio de México defines it as “al mismo tiempo que se avanza, a medida que se hace algo” (at the same time as one moves forward, as something is being done). Its example: “Resolver las dudas sobre la marcha” (to resolve doubts on the way).
Áhi se va, “there it goes.” The dictionary marks it as popular and explains it as “ya, así, como esté” (now, like that, as it is). People hacen algo al áhi se va, do something the there-it-goes way. Another example: “Entrégalo, áhi se va” (Hand it in, there it goes).