I have to agree with the "no casting under a Jeep"!
True, if Joe managed to unroll hip loop, underneath the jeep, he obviously never hit all the grime and line destroying debris on the Jeep's undercarriage. However, true, unless you already can "cast like Humphreys", I sure wouldn't try it! Of course, if you could ALREADY "cast like Humphrey's", this post would never have gotten started!?!
When I saw the famous spin caster and egomaniac "Ernie St.Clair", stand 75 feet away from a china tea cup, then with the flick of his wrist, he'd toss his little, rubber, demo-casting-plug, into the teacup.......... I was, like everyone else I suppose, "duly impressed". Until, I realized, that "There are not too many fish worth catching in your average teacup!" So, when it came time to learn to fly cast, I took to the water, only, as has been suggested here,already.
Sorry, but "lawn" does not load a rod, the way water does and can, so what are you really learning? No matter what I'd learn in practicing anyplace, but at this bridge that has you stumped, I know that when I got back to the bridge, the currents, the wind, the angle, everything...... would be totally different, than from where I'd practiced to fish it!??! :-D