Apple's new 'Intelligent Tracking Prevention' means that the first-party cookies used by Pardot will be deleted after 30 days of prospect inactivity in Safari 11. This is going to impact your ability to track visitors on Apple devices who visit your website less than once per month.
The first thing you should do is to check Google Analytics to see what percent of your visitors are Safari users. Typically this will be a higher rate for mobile than desktop visitors. If this percentage is significant enough to cause concern, the article below suggests increasing the frequency of your content and emails to more than once per month to keep visitors coming back to your site and keep their cookies active.
If all else fails and a significant proportion of your Safari audience let their cookies expire, do remember that any prospect re-visiting your site from a Pardot tracked email will be automatically re-cookied, and you can also use the Pardot forms on your website to re-cookie existing prospects in addition to new prospects.
What is Apple changing about cookies? In Safari 11, which is included as the default browser on the new macOS High Sierra, Apple is saying “we’re watching our figure, please hold the cookies.” They’re calling it “Intelligent Tracking Prevention,” and long story short, they’re deleting 3rd party cookies after 24 hours, and they’re deleting 1st party cookies after 30 days.