diff --git a/src/instruction.rs b/src/instruction.rs
index b6664e2..340bff6 100644
--- a/src/instruction.rs
+++ b/src/instruction.rs
@@ -74,6 +74,12 @@ pub enum OreInstruction {
     #[account(6, name = "mint_v1", desc = "Ore v1 token mint account", writable)]
     #[account(7, name = "token_program", desc = "SPL token program")]
     Upgrade = 5,
+
+    #[account(0, name = "ore_program", desc = "Ore program")]
+    #[account(1, name = "signer", desc = "Signer", signer)]
+    #[account(2, name = "proof", desc = "Ore proof account", writable)]
+    #[account(3, name = "system_program", desc = "Solana system program")]
+    Deregister = 6,
     
     #[account(0, name = "ore_program", desc = "Ore program")]
     #[account(1, name = "signer", desc = "Admin signer", signer)]
diff --git a/src/lib.rs b/src/lib.rs
index dbf8573..fc29e90 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,6 +14,7 @@ use solana_program::{
     program_error::ProgramError, pubkey::Pubkey,
 };
 
+// TODO Close proof accounts to recover sol
 // TODO Is downgrade necessary?
 
 declare_id!("mineRHF5r6S7HyD9SppBfVMXMavDkJsxwGesEvxZr2A");
@@ -41,6 +42,7 @@ pub fn process_instruction(
         OreInstruction::Claim => process_claim(program_id, accounts, data)?,
         OreInstruction::Stake => process_stake(program_id, accounts, data)?,
         OreInstruction::Upgrade => process_upgrade(program_id, accounts, data)?,
+        OreInstruction::Deregister => process_deregister(program_id, accounts, data)?,
         OreInstruction::Initialize => process_initialize(program_id, accounts, data)?,
         OreInstruction::UpdateAdmin => process_update_admin(program_id, accounts, data)?,
         OreInstruction::UpdateTolerance => process_update_tolerance(program_id, accounts, data)?,
diff --git a/src/processor/deregister.rs b/src/processor/deregister.rs
new file mode 100644
index 0000000..6d6c881
--- /dev/null
+++ b/src/processor/deregister.rs
@@ -0,0 +1,36 @@
+use solana_program::{
+    account_info::AccountInfo, entrypoint::ProgramResult, program_error::ProgramError,
+    pubkey::Pubkey, system_program,
+};
+
+use crate::{instruction::RegisterArgs, loaders::*};
+
+/// Register generates a new hash chain for a prospective miner. Its responsibilities include:
+/// 1. Initialize a new proof account.
+/// 2. Generate an initial hash from the signer's key.
+///
+/// Safety requirements:
+/// - Register is a permissionless instruction and can be invoked by any singer.
+/// - Can only succeed if the provided proof acount PDA is valid (associated with the signer).
+/// - Can only succeed once per signer.
+/// - The provided system program must be valid.
+pub fn process_deregister<'a, 'info>(
+    _program_id: &Pubkey,
+    accounts: &'a [AccountInfo<'info>],
+    data: &[u8],
+) -> ProgramResult {
+    // Load accounts
+    let [signer, proof_info, system_program] = accounts else {
+        return Err(ProgramError::NotEnoughAccountKeys);
+    };
+    load_signer(signer)?;
+    load_proof(proof_info, signer.key, true)?;
+    load_program(system_program, system_program::id())?;
+
+    // TODO Ensure proof.balance == 0
+    // TODO Send lamports to signer
+    // TODO Realloc data to 0
+    // TODO Reassign back to system program
+
+    Ok(())
+}
diff --git a/src/processor/mod.rs b/src/processor/mod.rs
index f1dd9cc..6807980 100644
--- a/src/processor/mod.rs
+++ b/src/processor/mod.rs
@@ -1,4 +1,5 @@
 mod claim;
+mod deregister;
 mod initialize;
 mod mine;
 mod pause;
@@ -10,6 +11,7 @@ mod update_tolerance;
 mod upgrade;
 
 pub use claim::*;
+pub use deregister::*;
 pub use initialize::*;
 pub use mine::*;
 pub use pause::*;
diff --git a/src/processor/register.rs b/src/processor/register.rs
index 4ad7c15..6b100ca 100644
--- a/src/processor/register.rs
+++ b/src/processor/register.rs
@@ -64,6 +64,7 @@ pub fn process_register<'a, 'info>(
         &slot_hashes_info.data.borrow()[0..size_of::<SlotHash>()],
     ])
     .0;
+    proof.last_deposit_slot = 0;
     proof.last_hash_at = 0;
     proof.total_hashes = 0;
     proof.total_rewards = 0;
diff --git a/src/processor/update_tolerance.rs b/src/processor/update_tolerance.rs
index c869f6f..6dfbfe9 100644
--- a/src/processor/update_tolerance.rs
+++ b/src/processor/update_tolerance.rs
@@ -5,7 +5,7 @@ use solana_program::{
 
 use crate::{
     error::OreError, instruction::UpdateToleranceArgs, loaders::*, state::Config,
-    utils::AccountDeserialize,
+    utils::AccountDeserialize, ONE_MINUTE,
 };
 
 pub fn process_update_tolerance<'a, 'info>(
@@ -30,11 +30,11 @@ pub fn process_update_tolerance<'a, 'info>(
         return Err(ProgramError::MissingRequiredSignature);
     }
 
-    // Overflow checks
-    if args.tolerance_liveness.gt(&(i64::MAX as u64)) {
+    // Sanity checks
+    if args.tolerance_liveness.ge(&(ONE_MINUTE as u64)) {
         return Err(OreError::ToleranceOverflow.into());
     }
-    if args.tolerance_spam.gt(&(i64::MAX as u64)) {
+    if args.tolerance_spam.ge(&(ONE_MINUTE as u64)) {
         return Err(OreError::ToleranceOverflow.into());
     }