Because of how NAT works, your public IP address is generally set at your modem/router.  You can phone up your ISP and request a static IP, and they might even help you set that up.  It'll probably cost at least $25 a month.  Or you can use a commercial VPN (who will sell your imformation to literally everyone and rat you out to the feds if you're posting hitler memes).  Or you can set up your own, if you feel like buying or renting a server.