how to ecure my dll being reverse engineered

Hi,
i wanted to know how can i secure my dll/exe being reverse engineered. I know the obfuscator tools like preemptive dotfuscator and others, i really dont want to use them, as in Microsoft VS.Net we the dll/exe but how could we save them being hacked, i mean to say writing our own custom algorithm or something, again i really want to code it, any help any direction would be highly appreciated.
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