限於

限 = 艮 + 阝 : Marie Curie (xi) caught the pope (阝) munching chewing gum (艮) in the anthill's bathroom (an4). Marie hates it when someone puts their chewing gum just anywhere in the room, so she marks a confined space with red and white tape and sends the pope to stay within the limits (限) while he is chewing.

于 = 亅 + 二 : Mnemonic symbol: prepositions (in, at, on, to, ...) are what glue the sentence together. Honey is as sticky as glue, so I'll represent 于 by a honey jar.

Yu the Great (于) was assigned to repair the electronics of the space station's kitchen (Ø2), but instead he was snacking honey from a honey jar (于). Unfortunately his capacitor (二) got stuck in the honey and now he has to use a crowbar (亅) to lever it out.