Hello Luis Jose, please excuse my late response.
Initial testing with robots suggest paper is too fragile, the landmarks at the middle of the field get damaged too fast, either broken, ripped or stained.
To be honest, I do not quite follow. As specified in the rules, middlefield landmarks should be positioned outside of the actual playing field. That is, any robot that would want to reach them will first need to position itself “out of bounds”. Given the maximal size of the robot (22cm) and the size of the “out of bounds” region at middlefield (30cm), any robot that would be able to reach the landmarks located there will have to travel at least 8cm during which it should have already been removed from the field (Section 1.10).
If the robot somehow manages to reach the landmarks and subsequently damages them, it is in direct violation of Section 6.1 (Fair Play), and by my reading of the rules can be disqualified from the tournament, as per Section 6.6.
Note that this is quite different from the normal issues with damaging the carpet/white lines, as it is quite obvious which robot is responsible. Moreover, it also is not comparable to damages that the goals many times incur, as while the goals can legally be reached during normal gameplay the landmarks can not.
Is there a list of alternatives to be/not to be used?
The spirit of the current rules suggest that the landmarks should serve as colorful marks of a specific fix point on the field. It therefore does not matter too much what material is used for their construction, as long as the colors stay close enough to those that are specified in the rules.
For example, we assumed it is not ok to laminate them (cover in plastic). At this moment we are evaluating the option of printing them on opaline paper.
As stated above, laminated landmarks are not a problem per se, but I assume that the plastic may create many reflections that will make detecting the landmark more difficult. Printing them on opaline paper may actually be a better option. If the paper-based landmarks are damaged often, however, I am not sure if creating them from any paper will help.
I am sorry if my (long) response does not help you much. I do believe that a problem like this should not be solved by technical means (i.e. by using a different material to print the landmarks on) but rather by the procedural ones (i.e. sticking to the rules and using the penalties specified in them when appropriate).
Please feel free to let me know if I missed something or answered from a wrong point of view – I’ll do my best to respond swiftly.