How can I add a tag parameter to Permalinks or Buy Buttons

[yotamcuralife]

Hello, 
Is there a way to set a tag on orders coming from specific cart permalinks or buy buttons?

I have couple of landing pages containing buy buttons and I want to tag orders by the landing page they came from. I want a more reliable way than google or shopify analytics to know how much conversions I made from each landing page.

Please Help 🙂