My horse is 15 years old. He's an ex-grand prix horse who won many many divisions in the US and Europe. I now do child-adult jumpers with him (3'3" - 3'7") and he still is very quick and wins plenty. However, he stops at the Liverpool. I know he must have done liverpools in his career because of the level he's at but he is truly terrified of them now. I can't even hack him near the jump that had the Liverpool beneath the jump without him trying to push away from it and this is a year after I started the work with the liverpool. We stopped for a while because he began being frightened of all blue jumps whether they had a liverpool under them or not. Now I have need of again trying to get him over a liverpool. Are there any tricks that anyone has to get him to be willing to jump the liverpool again?

Do a USEF record search, he may have always had this issue.
Not all shows use them and he may have only been shown in classes without.

But for training purposes try this;
Use a single pole [wood-for weight]
Honestly start @ walk, treat him as if he has never jumped before
Wrap pole fairly tight with blue tarp- and as above
When he can handle that much-use 2 poles and wrap tarp from poles on each end towards each other
Then start as above
Each time he gets comfortable, unroll the pole to expose as much of the tarp as you think he can handle
You may not be able to add a "fence" to it for awhile
Once Ok, I start w/ tarp @ 18" width back edged 2' verticle, then still @ 2' or 2'3, verticle with tarp behind, till finally tarp w/ verticle placed in center

If he is dangerous about it, the above can be done off a lunge.

Good Luck