Although I love to encourage creativity in my campaign, nothing irks me more than when people treat Tensir's Floating Disc like it's Tensir's Magic Carpet Ride. If you say, let people ride it across a blank of wood, next they'll try to ride it over a tight rope, and finally ride it over a single strand of spider web bridging some gap. Allow them to hover over water, and next thing you know, they're crossing chasms floating on the Oxygen molecules beneath the disc.
Simply put, TFD should follow 1 simple rule of physics: For any force there is an equal and opposite force. If you put X amount of force ontop of TFD, the dics must exert that much 'magical' force on the ground to sustain it's hover. If the ground cannot support that force, it gives way. This means TFD should trigger preasure sensitve plates, fall through water, and not fly through the air.
It's a Mule for moving stuff, not a mode of transportation.