We had this problem -- sororities stealing stuff. Alpha Xi Delta was particularly bad about this back in our colony days. It was understandable, we'd had a few guys 'captured' stealing their charter (they were returned to us after a reportedly horrific captivity in which they were led to believe their eyebrows were shaved and other torture implements were employed
). Anyhow, we'd steal things from eachother, and they'd of course fork our yard, put TP in our trees, etc. They had taken some pretty big stuff just as in the OP.
Anyhow, some of our guys decided to put a stop to all of this because it was getting a little ridiculous. In the early morning hours, 3-4 of our guys dressed of course in black and camo, ski masks and all purchased some hamburger meat. They went to the Alpha Xi house. Now understand -- the old houses in that area are not built on a foundation, I forget what it's called, but you can crawl under the house -- it's sometimes scary down there, snakes, skunks, etc.. but they were some brave guys. So they crawled up under that house with their raw hamburger meat and began to apply it to various spots in the house... and of course, they left.
Needless to say, the house began to develop an 'odor' about it. At first, they thought that some of their girls might have slightly 'less than clean' bathroom habits -- this turned out not to be the case, and I'm sure they bathrooms and other rooms were cleaned thoroughly -- but to no avail. The stench continued to worsen.
Week 2 -- their advisor from HQ visits. Likes what's going on with the chapter, good everything *except* the house just smells dirty. The chapter gets into some trouble (don't know how serious), and the next thing you know, our Pres. is approached by their crying Pres. demanding a truce.. Of course one was granted.
-- So realize that what a few of your girls are doing to this fraternity may come back to haunt you in ways you never imagined. And yeah, what 33 said -- if these guys don't retaliate, they're pussies.