The tag system for the pool chairs is an absolute joke (and not in a funny way). I honestly don't have a better alternative to suggest for Marriott, but the current system isn't working.
I was there in November (Thanksgiving week). Got up early the first morning we were there (couldn't help it - I'm used to it) and noticed people tagging chairs just prior to 7:00 am. My wife and I quickly got our bathing suits on and got to the pool by 7:15. Over half the chairs had been tagged by then. We tagged 2 chairs by the pool and went back upstairs to wash up and brush our teeth. When we went back downstairs at 8:00 am, the 2 chairs we had tagged now had a second tag on them, in addition to ours. While we were standing there wondering what the heck happened, a family walked up behind us and proclaimed the chairs to be theirs since their tags were on them. They didn't want to hear that we had put our tags on them first and got very argumentative. Not wanting to get into an argument at 8:00 am on my first day of vacation, we let the rude family have the chairs.
We walked over to another set of chairs further from the pool, tagged 4 of them, and my wife went back upstairs to get the kids, and I went to get coffee. When we returned about 15 minutes later, another family had set their stuff on 2 of our chairs (but at least our tags were still on them). When I picked up the stuff to get it off of our chairs, a young mother YELLED over to me to put her things down and that those were her chairs. I calmly explained that the tags were mine (too early in the morning to argue). She continued to rant that someone (I guess she meant me) had removed her tags from the chair. I know I didn't, and the tags on the chair were mine, so I just sat down. She continued to rant loud enough for anyone to hear, but oddly enough, her husband, who was standing right next to her, wasn't saying a word. In fact he looked embarrassed. I let her continue to rant until she must have felt foolish enough to stop. I can only guess that she really didn't tag them, and had intended to intimidate the person who actually did. In this case it didn't work.
If you go during a busy week (like Thanksgiving), my only advice is to get up REAL early (people started tagging between 6:30-6:45am all week), tag as many chairs as you need, and, this is real important - don't leave the chairs until the tagging process is pretty much complete.
As an aside, I thought the palapa reservation process was pretty painless. Takes a while standing in line early in the morning, but far less aggravation.