Help me Help my cat's before they croak.?

"At wit's end. . . .I have (3) cats (17lbs gray tabby 6 yrs, 14 pound tabby mancoon mix 3 yrs and a 13 lbs white,tabbymix 6yrs. How can I get they to quit swallowing ("fishing line ,dental floss,thread and today the white one "Mouse" had half of a 4 inch piece of hard plastic hung in his throat and I heard him gagging had to grab him and pull it out.Tis is a constant battle with them doing this. Vet's charge anywhere from $650.00 to $850.00 to split em open and get the crap outa their intestines.("(I know cause a cat I had 14 years had it done. These cat's are totally inside,netured and spoiled rotten but I luv em. Pulaaleeze help me figure out how to break these boys from doing what's gonna kill them sooner or later. ANY HELP APPRECIATED. . . sincerely ,Johnathan Hemlock