A week from Saturday, NFL teams and agents for players who will become unrestricted free agents are allowed to begin negotiating. But they can't sign off on a deal until 3 p.m. CT on March 10, three days later.

This, of course, causes concern among those of us who need official NFL-approved COUNTDOWN CLOCKS!! to get through our year. While we figure out whether to set ours to March 7 or 3:00.00 on March 10, we'll toss out over the next two days one person's list of three do's and three don'ts for free agency. (And, yes, there are always going to be exceptions to every do or don't.)

There should be more don'ts than do's in free agency (see: 2014 Free Agency "Winner" Tampa Bay), so we'll start with the don'ts today and finish with the do's on Thursday:

Free agency DON'T No. 1: NO ONE OVER 28.

Don't fall in love with the past. Players are either getting better or getting old. The league's great personnel men have no rear view mirrors and a keen sense for Father Time's tipping point.

Generally, 30 is the frowned-upon age in free agency. The frown here is directed at anyone not coming off his rookie contract. Twenty-seven tends to be the perfect intersection for necessary youth, experience, hunger, upside and reliable durability.

Free agency DON'T No. 2: NO RUNNING BACKS.

I'm not devaluing the position. I think it remains an important position in a league that's not only pass-happy, but pass-rusher-happy. If nothing else, someone has to keep the pass rushers honest and the extra DBs from flooding the field and staring down the QB.

However, I just think, as a general rule of thumb (Note: General rules of thumb don't apply to a certain 2012 league MVP), there are too many other avenues to acquire younger running backs who can make an immediate and acceptable impact, and are less likely to break down during a long season.

It's an unfortunate "don't" for a guy such as Demarco Murray, but that's just how it is. His great season in 2014 included too many touches for it to work in his favor in 2015. At least not from this vantage point.

As I said earlier, there are exceptions. Peterson would be a classic exception to the first two "don'ts." In a risk/reward scenario, I'd push the chips toward Peterson's talent and determination.

Darren Sproles was another good exception a year ago. He was a running back turning 30, but he also was still very much the toughest and most unique matchup at running back in the league.

Free agency DON'T No. 3: NO KNUCKLEHEADS OR INJURED PLAYERS.

Building a roster is difficult enough without having to count on knuckleheads not to be knuckleheads for seven months. Just ask the Browns.

Last fall, the Vikings needed a no-name receiver — Charles Johnson — to come out of nowhere to help them fill out a pro-caliber receiving corps. We all bundled up the fault for this and dumped it at the feet of Cordarrelle Patterson, who was slow to understand the mental commitment needed to succeed at this level.

What we all should have done was take a big chunk of that finger-pointing and direct it toward Jerome Simpson, a classic knucklehead who couldn't graduate from Knucklehead U.

Simpson seemed like a good dude, but he came to the Vikings via free agency with a proven track record as a knucklehead. He even had the jail time and the impending NFL suspension to prove it.

He messed up again. Got another suspension. Messed up while on that suspension and was tossed aside quietly while the team dealt with the Peterson fiasco last season.

When the roster was put together, Simpson was counted on to help out. But, predictably, he did what knuckleheads tend to do: he wasted a precious roster spot and left his team scrambling to fill a hole that's not easy to fill during the season.