Ad Script Integration for Static Site

I need a small but precise job done on my purely static website: insert an advertisement script so that it loads correctly on every page without slowing anything down or disturbing the existing layout.

Here is what I’m after:
• Place the ad code in the optimal spot (likely the head or just before closing body) and make sure it loads asynchronously.
• Verify that the script fires on all pages and displays ads exactly where intended.
• Keep the current HTML / CSS / JavaScript untouched beyond what is strictly necessary.
• Provide the updated files or a clearly marked code snippet plus a short note that shows me where you put it, so I can replicate the change later.

If you can check the console for errors and confirm normal page-load times afterward, that will be my acceptance test.

The site is live, so accuracy is important; once everything looks good in a quick staging copy I’ll push it myself.