You can also replace ads and banners with a few of SafeSquid's built-in templates, instead of creating an htlm file to replace them.
Try using these built-in templates -
checkeredgif - appears as a small grey dot in the upper left corner
uparrow - appears as a small uparrow in the upper left corner
downarrow - appears as a small downarrow in the upper left corner
To use these templates, just replace the 'Template' option in the rule under URL redirecting, e.g. -