At many mixed-use airfields you may find that arrestor cables / hook barriers are installed on the runway, these may present a hazard to a landing or taxiing aircraft. They are thick (roughly 6 cm diameter) steel cables and should only be crossed slowly. If you know what to look for these are easy to spot - on both sides of the runway there will be a (usually yellow and black) shack housing the retarders, additionally there will be a lighted sign (yellow circle in a black box, same colour scheme as the 'runway remaining' marker boards).
When approaching an aerodrome with hook barriers it is advisable to ask the tower if and where they are active. Since they are meant to provide overshoot protection for military aircraft they will usually be found at the departure end of the runway, nevertheless they can be active on both sides as well!
Needless to say the distance from the threshold to the cables should be subtracted from TORA and LDA for performance calculations.