Proxies not allowed for some web sites?

[ThankgodforRB]

I live in Canada, but travel to the US frequently. I'm trying to log in to a web site (pinnaclesports.com) through a proxy, but when I try to log in the page just resets to the same page without my login information populated.

Are web sites able to detect the use of proxies and deny log-ins if people are on them?

Is there any way around this?

[Freakin]

I use VPNs and don't have a problem with it. You won't find free ones though