Persistent hyperlinks in Calendar Events?

The Church-wide events regularly have hyperlinks to lds.org, the mormon channel, etc.

How can we do this on our ward calendar events? I have tried adding html code, and oddly enough it works one time, but the hyperlink disappears after it has been clicked the first time. The code I'm using looks like this:

Is there an answer for this? I would like to do this as well and link conf talks for our weekly lessons.

BTW, I just noticed that the links are active in my email notification. It is a product of my email client, but an interesting point and does provide attendees with a link.