All of the landing pages that we have built through Marketo that are on our website show up as a broken link on the alexa.com audit. How can I fix this?
"Built through Marketo" but "on our website"... are you IFRAMEing them? Please provide example URLs.
Those links aren't actually broken (you can test them yourself). It looks like Alexa is peeking into the <noscript> variant of your Marketo form (which is fine in itself) and both misidentifying those as followable links (they are not) and as broken links (which they aren't, even if they were links).
This is a bug in Alexa.
That's not a broken link. It's a POST acceptor so you shouldn't be able to GET it.
/save is the Forms 1.0 and noscript forms endpoint. They have no business following it as if it were a link. So again, an Alexa issue, not a broken link.