If a Lithium does leak...you'll know. I believe Lithium combusts once exposed to air. I may be mistake, though.
(NB: I'm not a battery chemist, or any kind of chemist. Nor am I Blast.)
Metallic lithium, I'm told, combusts on contact with damp air. According to the datasheet Energizer Lithium batteries use a Lithium / Iron Disulfide chemistry. As far as I can Google this chemistry does not spontaneously combust.
Lithium CR123A primaries can "vent with flame" (that's explode in layman's terms) under some conditions, specifically if they're recharged, put under a very high load, short-circuited and/or there are multiple cells in a device with significantly dissimilar states of charge (this can lead to recharging of the more-discharged cell). Don't do those things.
A single-celled CR123A device with no capability to recharge should be reasonably safe -- I carry one in my pocket every day. I use a pulse-load battery tester before installing cells in any multi-celled CR123A device.
Today I've read reports that lithium primary AAs and AAAs can do the same thing under a 2A+ load or very high temps (140 deg F and up). I don't know how true these claims may be. I've also read that there was a brand of lithium primaries that used the same chemistry as CR123A batteries and were taken off the market in 2006. Before today I've never heard of lithium primary AAs or AAAs doing the "vent with flame" thing.