Poles in gateways. All my gates have coloured poles on the ground in them, the foals learn from Day One to pick their feet up.
If they are older horses (and non are used for jumping anyway) occasionally I put the pole up so that it is about a foot high, fixed. No problems. They either walk, jump or fall over it, if they are clumsy or lazy they only trip over once. Lesson learned.
I never have any problems on hacks with them having a silly hissy fit about a log on the floor.