If you're playing in freeform or using the money cheat then I highly reccomend using
no gates in the fences, and sticking 1 zookeeper in each exhibit. When you do this make sure you assign them to the exhibit they are locked into also, so they don't try to clean up other exhibits and complain they can't reach the site.
They still occasionally have problems keeping up with the animals but the zookeepers do a lot better. They tend to walk through exhibits trying to get to other exhibtis around the zoo, so having no gates really does help a lot.
If you are not using the money cheat then make sure your zookeepers are assigned only to a few exhibits, and if possible lock them away from the guest area by creating gates between adjoining exhibits. This should stop them wandering too far away!:
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As for the guests getting frozen that happens to me sometimes too, and I do find it very irritating
- sometimes looking at theire needs (hunger thirst etc) and putting them near where that need can be satisfied breaks them out of the cycle. Otherwise I find closing the zoo, emptying it of guests and then re-opening can sometimes do the trick. Sometimes saving the game and reloading it will also make them active.
Hope this helps!