Securing anonymity technically
An employee survey stands or falls on trust in anonymity. If answers are perceived as traceable, they will not arrive — or only the polished ones. The "anonymity promise" is not enough, it must be technically verifiable. Concretely that means: no login, no plain-text IP storage, no timestamps that allow reverse inference.
Technically this can be implemented with three measures: a hashed submission token (instead of user ID), hash of the IP address with daily rotating salt (instead of plain-text IP), aggregation of submission time to day-level granularity (not seconds). You can still detect spam (rate limiting via hash) but nobody can map an answer to a person — not even the admin.
Communicate these measures openly before the survey. "We store only a hashed session ID, no IP, no timestamps to the second — see technical details" creates more trust than a generic "your answers are anonymous". For sceptics: disclose the data model, e.g. as a screenshot of database columns. Anyone transparent has nothing to hide — and gets more honest answers.