if its a mvc application
@Url.ContentUrl(Model.Url)
should return you freindly urls

Regards
/K

It is a webform application. The quick and dirty way will be to write an extension method something like

public static string GetFriendlyUrl(this Url internalUrl)
{
string url = string.Empty;
if (internalUrl == null || string.IsNullOrEmpty(internalUrl.ToString())) return url;

var urlHelper = ServiceLocator.Current.GetInstance<UrlHelper>();
var friendlyUrl = urlHelper.ContentUrl(internalUrl.ToString());
return friendlyUrl;
}

and instead of writing

<li style="background: url(<%= this.CurrentBlock.BackgroundImage %>) no-repeat 0 0;" >

Write

<li style="background: url(<%= this.CurrentBlock.BackgroundImage.GetFriendlyUrl() %>) no-repeat 0 0;" >

But I don't want to do that. I want to override the rendering mechanism so that I don't have to do this at all the places and can handle it at a single centeralized place

You can add a readonly property in your block to render url as you want and use that property instead.

Regards
/K