Kendra: In Grease, Danny and Sandy first sang, “Summer fling, don’t mean a thing,” but even they quickly discovered how easy it is to end up “Hopelessly Devoted.” While summer hookups can sometimes stay by the shore, feelings after vacation relationships tend to come home in your suitcase.

While expiration dating can be “fun” in theory, there are inevitable repercussions for summer hookups without meaning. However, with a few set guidelines for summer relationships, you can avoid confusion and danger.

• Agree on a timeline. Some relationships are just meant for a season, while others may be meant to last beyond summer. Either way, summer couples should agree on either an endpoint to their relationship or agree not to end it at all when August comes.

• Define the relationship (DTR). While I believe it’s necessary to “DTR” all relationships, summer flings tend to have the murkiest of lines regarding exclusivity. Although it may seem easier to keep things casual, not being on the same page about where the relationship is heading can lead to end-of-the-summer heartbreak.

• Be safe. Summer romances may be fleeting, but they can have lasting effects. STIs and STDs run rampant year ’round, so don’t avoid serious dialogue about protection. Protect and respect your heart, but also your body.

• Don’t lie about who you are. Remember the trouble Danny got into because of his differing personalities with his classmates and with Sandy at the beach? Let your summer hookup partner fall in love (or even just like), with who you really are.

• Keep checking in. Be self-aware of your feelings for your partner and how they develop throughout the summer. While you may agree on ground rules at the start, another discussion about your future should occur midway and again at the end of the season.

So have fun “Summer Lovin,'” but make sure he or she is “The One That [You] Want.”

Wes: In my constant, and at times desperate, battle to keep up with modern “dating” trends, I find myself continually falling back like a frontline soldier of love in a full but orderly retreat.

One of my current fallback positions is the “time limited romance” Kendra describes, regardless of season. In my version of reality, couples don’t have to be together forever nowadays to enjoy the benefits of relationship. But things do go better if they’re in a clearly defined dyad before taking the relationship to next level, sexually.

Unfortunately, teens and young adults increasingly regard that view as rather quaint. Many kind of like hearing about it, but at times I get the impression that I remind them of that old guy I remember who sat around the bowling alley in Western Kansas regaling us with tales of the dustbowl. It was interesting to listen to, but really really old news.

So, in an effort to move myself somewhere into the 21st century — where nearly all my clients formed their relevant memories–I have begun suggesting that young couples retain the boundary of monogamy for sexual expression, but set an expiration date at which point they can revisit the viability of their love. This time-limited approach seems to scare them less, which actually encourages them to go exclusive, particularly young men who are even more afraid of long commitment than ever before. And besides, that’s by far the most statistically likely scenario. Why not be honest about it up front and buffer the inevitable heartache?

Do I like the idea of chopping off young relationships on some arbitrary future date? Not particularly. But in the end, therapists, advice givers and parents don’t actually get a vote on these things. We can only try to influence and guide teen culture. And if I do get to choose between random unattached hookups and something that mostly resembles a healthy, exclusive relationship, I’m going for the latter every time.

Yes siree. I remember back in the day, we used to have this thing we called “goin’ steady.” It was darn fine too. Why, we even did stuff like takin’ our steady to prom, we did. Grab a few quarters from the register, kids. We can play a little pinball and I’ll tell you all about it.

Wes Crenshaw, Ph.D., ABPP, is author of “I Always Want to Be Where I’m Not: Successful Living with ADD & ADHD.” Learn about his practice Family Psychological Services at dr-wes.com. Kendra Schwartz is a Lawrence High School senior. Send your confidential 200-word question on adolescence and parenting to ask@dr-wes.com. Double Take opinions and advice are not a substitute for psychological services.