When I saw that in a provider's ad, I had a pretty strong hunch of what she meant. Yet if you google the phrase you don't get any hits about anal sex, just, um, things some people consider fun.

Put something in like Trips to Greece.

or some other allusion to foreign or island travel.

Some of the euphemisms that are common include: cruises to the isles or to the mediterranean; languages spoken, French, Greek; "A" level, add $100; PSE sometimes means this, but others think it means BBFS, so watch out.  Hell, why not just say, "I love to get my butthole pounded?"

making a reference to Santorum, they'll get it.

I hope you don't actually think "keeping the innuendo low" on your website will be any help to you legally should you have that kind of problem. It won't.

Not that I expect anyone to advertise "fuck my ass for an extra $50", but just saying "Greek" or making some mention of Greece seems to work for everyone else.