the jumping really isn't species-specific with gars...if you have a fish in a tank, be prepared for the possibility of it jumping out. period.
gars are good jumpers, so they may warrant more attention. tape will work if you have glass tops and tape the corners down (i do this on my 120g). on my larger gar tank i have an entire old bed frame on top of the tank (collapsed into two rows)...this gives appropriate weight and weight distribution so the gars can knock off the tops. gars are quite strong, make sure you have heavy tops and something to weigh them down that will not damage the entire tank if it's knocked off.
good thing is that since they breathe air, they have a bit more of a fighting chance if the gar jumps out while you're gone!--
--solomon